As to why there isn't an advanced class bonus roll or something... Personally, I like rolling need on dps / other gear if my companions can use it AND NOBODY IN THE GROUP ROLLED NEED. I believe it's perfectly fine to either watch the rolls go and need on whatever you want if nobody cares, or ask if you really feel obligated. An advanced class bonus to your roll might impact the ability to get gear for when I respec or to gear out my comps. It's a small issue, but it's there nonetheless..
That doesn't really make sense, because if the person doesn't Need it, they'll roll Greed or Pass. So you can still Need and get it for your companion — you just can't get it over someone who would actually be equipping it for their player character.
If your argument is, "But now stuff might get ninja'd from my companions when everyone's fully geared!" ... well, I'm sorry, but I'm going to argue that is an astronomically more trivial concern than stuff getting taken from actual players to feed a disposable NPC used only on solo missions or gimmick FP runs.
As for "when you respec", no one changes what armor type or primary stat they use when they respec. So that's just flat-out a non-issue.
I agree that WoW's solution — gray out the Need button completely for certain classes — is ham-fisted and unpleasant, and prone to mis-categorization errors locking out legitimate gear from people. IMO, the "+100 to your prime stat rolls" is the correct solution here and would basically close the topic down completely as far as Group Finder is concerned.
A guild can never be available 24/7 in all levelranges so groupfinder is a must for the majority of the playerbase.
This is true, as I've said I play at completely unpredictable times so while I do have people I like to group with, they're not always available / online. And sometimes, it's just fun to meet new people — I've met a lot of cool people in Group Finder.
I guess my opinion here is that while yes, ninja'ing / etiquette issues are always a danger in "blind date" gameplay situations like Group Finder — that doesn't mean you should deliberately ignore a chance to improve the system. And a +100 bonus to prime stat rolls is am improvement with near-zero negative repercussions that would flat-out solve the issues almost completely.
You would still have people taking gear they don't actually need anymore (just to take it), or friends/guildies of the same class Needing everything to hoard for themselves, but these are more minority situations and they're also almost impossible to identify / sort out mechanically. So this enters "lost cause" territory.
On the other hand, It's essentially impossible to be wrong about a Marauder rolling Need on a Heavy Aim chestpiece.