Good discussion here, but the thing I'm going to nitpick about first is that ANet has used the term damage instead of offense. Not sure how dated that is, but it's the one that's been used on both GW wikis, iirc.
I suspect there's a big disconnect somewhere along the line. I don't think roles should be thought of in terms of "this class fills this role, that class fills that role"; rather, think of them along the lines of skills. For example, a sword warrior has the capability to bring damage, support, and control; however, if all he does is spam 1, all he's doing is damage. That's not very supporting or controlling!
GW2 moved away from GW's stance of "everything is group content forever (unless it's in the tutorial area)". This had a major impact on the builds they made available to players: because combat is determined by damage done, every class must have the capability to deal enough damage to turn the tide of the battle. Builds without this capability are flat unable to succeed in solo combat. By extension, every class and every player is capable of dealing (and, possibly, required to deal) significant damage. If you're not sure what you should be doing, pressing the 1 button is a good start.
In the strict sense, support means "making yourself or your allies better, or preventing bad things from happening to them" and control means "making your enemies worse, or preventing them from doing things", but as Drake went over earlier, there's a lot of overlap. My favorite example is cripple - you can use it on the guy you're trying to kill so he can't run away, or you can use it on the guy going after your friend.
It's going to be very hard to make a build that only fulfills two roles, and I suspect impossible to make one that can only deal damage, but that doesn't mean you're forced to fulfill all three roles. It's just more effective if you do - and while you can get
pretty close to making a build that only does damage (disclaimer: I don't traits at 1 am), I don't expect that to be the mark of a skilled player.
As for min/maxing, it's going to happen. The game expects you to be versatile and able to respond to many different situations, so the build that can respond to the most situations (and the most common ones) best will be superior. You can argue that the delta between builds will be smaller than other games, and I'd agree with you, but that doesn't mean that, for example, the greatsword warrior isn't going to do more damage, be more mobile, and overall be more useful than another build. To claim that min/maxing won't exist is to claim that everything about the game is perfectly balanced, and the game is far too complex for that to ever be true. I hope, however, that things will be balanced enough that the ability to use your skills effectively will be more important than which skills you choose to bring - not that your choice of skills should ever be unimportant.