The thing about this, is that PvE characters are more story-related, and the game requires you to spend time and money to get your character to be really flexible. If you're rich, you can buy all the skills you need for your new secondary at Ember Light Camp.
PvP is all about Faction, and you can always unlock skills, runes, mods of any class at any one time, that's why it's shared across the board, because you already have access to every skill, rune, and mod.
In the PvE world, where there is an economy, the purchasing of skills acts as a necessary gold-sink. If the economy didn't have gold-sinks, then there would be an abundance of money which would throw the economy out of whack.
And also, about the PvE world, is that it's a story about your character that you made. Each and every PvE character is a new tale about a new hero, no matter how corny that sounds. Think about this analogy for a second...
Say that in University I am studying for a degree in Architecture, and have taken two years of, say, Chemistry. Then, my friend is getting a degree Mathematics, while minoring in say, German linguistics.
Now, what if I chose to change my Chemistry, and decide to try learning German linguistics? I can't just talk to my friend and have everything he has learned just suddenly appear in my mind.
Now, I know what you're going to say, wah wah, it's a game, blah blah. But, the analogy makes sense since PvE characters are more story-line based than PvP made characters. PvE is VERY VERY different than PvP. PvP has no economy, no gold-sinks, but there is still the grind in unlocking everything, whereas in PvE you can just buy every skill for your character.
There's more to it, but I believe I've discussed it enough to get my point across.
/notsigned