Dragging this post up from a while back, but could you elaborate on this point?
Well, the problem is really two things, though from what you describe we're only looking at one of them.
One of the problems with talent trees in many games is that they are used to hold unlockable abilities. These tend to change the very essence of an RPG. Instead of having numbers that determine how good a character is at the various possible interactions in a game, the abilities themselves are the interactions. This makes characters far less comparable to one another, and it makes it far more tricky for the player to cope with opposing characters who have abilities the player hasn't even seen or tried out. Furthermore, it makes it tricky for the developers to implement large scale game mechanics that affect each character to varying degrees. If a game relies purely on an ability/talent tree and does away with numerical statistics entirely, the developer has nothing to work with in terms of, for example, altering the cost of items based on the customer. Developers have to scale back on the number of formulae that can be used on all character in favour of formulae attached to unique abilities that a character can either have or not have. In other words, numerical statistics aid simulation far better than unlockable abilities.
The second problem, which is more applicable to you, is the tree itself and whether it's advantageous to structure progression in such a way. What trees do is linearise progression. Requiring one thing to get another thing may be appropriate if it matches up with real life skill requirements, but in a lot of games it tends to be very arbitrarily put together, though mostly in games with unlockable abilities like Diablo II. Instead, I think there's almost always a more appropriate way to go about structuring progression. Mixing up training, use-based levelling and point allocation while having very shallow hierarchies (such as spells inside spell schools) tends to be far more appropriate for most games than deep hierarchies.