Class talent trees

This is just going along with the idea I had from another post where each class only had two separate trees to branch into. I was thinking that maybe each class started as a regular old whatever, and the split to which side you wanted to take would happen at a certain level. Or a middle set of skills that each role has access to?

Going with the apothecary example, it'd be something like:

(Low Level)
medicine vial (heal self or ally nearby)
blah blah blah
/----------------\ <--------------level whatever split
(DPS)------------(Healer)
Harpoon---------Throw vial (medium-range heal)
(chunk that spear)

*This is a terrible ASCII chart.*

I'm using actual abilities as the talent tree instead of "perks" like in WOW and other games. Would it be preferable to do it this way, keeping the different specced classes from having access to the other skills, or would it be better for each class to have access to all of their skills, but spec differently so they're better suited to using certain abilities (like WOW)? Really though, I'm more of a single-player rpger than an MMOer, so I keep going in that direction.

I've seen MMO's with both. So, ot's just whatever we decide to do. MMO's should be fairly simple to get into, that's the biggest challenge, I think. We may be considered Hardcore gamers, but our audience isn't most of the time. That's why I really feel like we should go the route of chrono tales and city of steam, with the browser/lightweight client. Simple to get into. No big downloads= more fanbase access.

As far as skill trees goes, I'm down for whatever. I wouldn't mind a leveled talent tree, with passives every so often tho. Where you can put 2 points in Harpoon and one point in Throw vial, etc. Give them so many points per level, and let them figure out what to do with them. Kinda like Diablo 2 or something. Here's some categories, you choose.