Honestly, I think the biggest difference is the players in BB versus HT.
Hattrick started out as a very simply game engine and the players were and for the most part are 1 dimensional. The value of a player is largely dependent on his primary skills and with the addition of secondary skills, that really determines how he is capable of being played. In fairness, they've tried to move towards a match engine that requires more multi-dimensional players...but its still fairly simplistic compared to real soccer. I don't know, maybe that's the way they want it, they've always prided themselves on being a game were casual players can excel.
In Buzzerbeater, the players have more dimensionality. Do you want a guard that can shoot? pass? with inside skills? with rebounding? with high potential to train 'em up? If he has decent inside skills, can you play him at the 3? etc.
In fact, if I had my choice, I'd move for a potential/training/salary system that resulted in more skewed players. Even in Buzzerbeater, there tends to be to many centers with the same IS, ID and Reb. In RL, there are a lot of players that are good defensive players or offensive players, but lacking the other area, yet in the NBA or college they serve an important role on the team.