That's the first thing that crosses their minds.
It's not a bad thing, good games and good sales can coexist just fine.
quite a lot of studies and books have been written over the subject)
What's your game's target audience? - the hardcore gamer, the casual gamer ?!
You want a guys game, girls game, both guys and girls, family games ...
For what type of mentality - conqueror, merchant, wanderer ... [you want your game to be played by everyone and each player to find something fun to do, no matter what their expectations are? or do you want to make a great game for only a small part of the market]
>> from what I recall .. the conqueror wants to win, merchant wants to improve himself, wanderer wants to see everything .. and there were more types that escape right now ...
Also there was a measurement in dimensions for each game:
- pacman: 2D
- king of fighters: 3D
- quake1: 4D
- 3d shooter in which you can lean over corners, etc... : 4-5-6D
etc etc ..
(these are not the exact numbers, I'm sure I'm way off, but the idea stand: the more actions and buttons you have to perform and use, the more dimensions your game will have. the more complex, the less players will fully understand and enjoy it.)
the list of questions goes on.
At the end .. what sells most likely will differ from what one originally envisioned as his perfect project - and he either adapts, or finances the project himself from his pockets (funny fact: no matter the game, at the end some players will curse him from making bad decisions they don't agree with).
So if he's sitting on oil .. he might finance his ideal game. Companies don't have the luxury of acting like starving artists for the sake of a good title, unfortunately.
And you can see this all around you. Nintendo made a lot of money with Super Mario back in the day, because it gradually introduced new challenges and abilities, and the gameflow was easily understood by the players. Blizzard adopted the same style: strategies give you one new unit per mission, WoW gives you 2-3 new spells per few levels, letting you play with them for a while before giving you new ones...
Also they tried to make a game for everyone:
hardcore? > raids.
not so much time? > heroic achievements.
want to keep improving yourself with limited time? > arenas
a few hours every 3-4 days? > lousy profession epics but still enough to feel rewarded for playing.
What sells is important for a company that can lose everything with a few unlucky releases (see Flagship: form, work on a big project/Hellgate, fail, close down studio).
I'd like to see a developer not taking into consideration these points
And finally .. related to Heroes: I hope they can make a product that sells AND meets our expectations at the same time.