The question was raised as to why HOW (unlike TFT) does not have rules for raising Attributes with XP. Instead XP can only be used to purchase higher levels of skills/spells.
Here is the official, and well known, historical primary rule for games of this type:
If you do not like a rule, feel free to change it!
I sincerely mean that! There are no game police so tweak rules to fit the way you want to play!
Now that being said, here is why I do not, and will not, create an official option in HOW to increase Attributes through XP: It breaks the spirit of the game and IMHO ruins it. Those familiar with the Melee/Wizard/TFT system will also be familiar with Conan the Librarian wizard. Attributes could be raised to 20+ and as ST powered Wizards spell casting, they would have a high IQ and a Conan like ST in order to cast spells. It broke the game for me mechanically and conceptually. I was determined not to repeat what I saw as a design mistake. I think as conceived originally, Melee/Wizard was a terrific pair of fantasy boardgames. It was their conversion from boardgame to RPG (with TFT) that the game system (IMHO) broke down.
Remedy part 1: Adding the EN Attribute, this effectively got rid of the Conan the Librarian Wizard while adding a heroic sense of taking damage and being able to bounce back the next day.
Remedy part 2: Allow Players to increase their skills/spells but not their attributes. This avoids the I am good at everything DX/IQ munchkin gaming that I saw(and hated) abused in games of TFT. Instead Players now focus on the character and how to grow their abilities (skills/spells) with XP. Just Attribute dumping/increasing does not focus a Player on developing their Hero into being a better blademaster, a master of void elemental summoning, or becoming the greatest archer EVAR.
You see in using the the HOW method (XP increases skill/spell levels only), Players are developing a class for their character! By electing to hone known skills/spells and choosing specific new skills/spells, each Hero is become a specialized class or individualized Hero of the Player's design.
Sure you could say, "well Attribute XP increasing and just buying a skill here or there its all the same thing in the end anyway." Sorry but I don't believe that is strictly true. This method oversimplifies the character conception and building process over long term play, thus robbing Players of the unique building aspect of creating their own Hero.
Second, not allowing Attribute increases requires Players to rely on each other, and/or retainers! If I cannot be good at everything I do DX related, then it requires different specialists to come together to make it through an adventure. This again mimics the philosophy of class based game experience without the artificial barrier of your class can/cannot do task X. Instead the Players get to decide through their own Hero's skill/spell focus what they can or cannot do.
You may disagree, and you may have alternative options, and that's cool. I am all for you house ruling whatever you like to make the game fun for you! I'd only suggest trying it as written for awhile. You can always go back to a more TFT'd version, but you might also be pleasantly surprised! In the end, do what makes the game fun for you!
I am at work on the Faults & Favors rules for Blades & Black Magic. In essence taking a fault gives you a Hero point, and you could use that to buy a Favor (special ability) or add a point to an Attribute. Currently a 3 Fault max is my play test. In design I always default to Heroic, not Super Heroic, characters and game playing.
As to Heroes being underpowered vs. average humans. Starting Heroes have 42 pts of Attributes and have a bonus 4th attribute. Average folks have 24 points, no EN, and that roughly makes Heroes worth 2 average folks. That's heroic, but not super heroic, and still keeps a group of bandits challenging and not simply a speed bump on the road to Bel Turhain Moor.
I liked the Melee/ Wizard system specifically because characters did not become what they ended up being in D&D: god challenging, dragon riding, magically encrusted fops. There wasn't a point in Melee/Wizard/TFT gaming when dragons became boring, or Kobolds became like milkweeds to be easily blown out of the way. Enemies of any kind were something to be respected because your character could quickly die. EN (in HOW) is a way to make Heroes (and special villains) more hardy while still making them subject to the ever present mortal coil.
I called characters Heroes for a reason: they are built to be heroic and to do/dare more than the average NPC in the game. I did not want them to become Super Heroic because the game breaks down, becomes boring as nothing is challenging enough, and IMHO it ceases to be any fun. In the end I made the game I always wanted to play and it reflects the kind of Heroic stories/gaming (not super-heroic) that I really love! I can only hope it may be something you'll like too.
Thanks again for your interest and for giving HOW a try. I really am grateful for your support, questions, comments, and appreciate the differing opinions.