Question

If you don't want to buy all the mini expansions (Factions, nightfall, etc) but you have the original(prophecies), and you're thinking about picking up the game again with buying the real expansion(Eye of the North), won't you be behind because you didn't unlock anything from the mini expansions? isn't Areanet sort of FORCING you to buy all of its releases to stay on top?

The three original releases (Prophecies, Factions, Nightfall) are all stand-alone separate "chapters" (as Anet calls them), none are required to play the others, or Eye of the North. Yes, you won't have as massive a selection of skills to choose from as you would if you owned all three campaigns and the expansion, but it's absolutely possible to play with just one campaign's skills and "core" skills (which are available from any chapter, regardless of which other ones you own). A few are generally considered "nice to have", but none are really "required".

PvP is the only aspect where you might run into some problems, and even then, it's not generally considered necessary to have -all- the campaigns. Even so, it's still entirely possible to play most PvP without problems (there are no skills in Factions or Nightfall that -require- Factions or Nightfall skills to counter them)...high-end PvP, you're likely to run into snags, but that's to be expected, since the whole point of it is to stay on top.

Depends on what you do in-game. PvE, not really. PvP, yes.

Yes. It's called marketing! Anet IS in the market to make money after all.

It is definitely doable to play EotN without the other two campaigns. Here are a few disadvantages that come to mind off the top of my head. They aren't insurmountable by any means, but maybe they can help you make your decision.

1) No heroes from Nightfall - this makes solo playing a little more difficult. Henchmen are not nearly as strong as heroes since you cannot add runes and inscriptions to their armor, pick their build, or give them good weapons. But a lot of the game is still extremely difficult even WITH heroes. You might as well get used to forming parties with guildmates or PUGs anyway. You will slowly acquire heroes in EotN, but you have to work with what's given until you have a good selection. For example, you don't get a nec until late down one arm of the story (staying vague to avoid spoilers), but my MM was a tremendous help getting through the rest of the game up to that point.

2) You cannot cap skills from other campaigns, even if you kill a boss carrying that skill. The biggest thing is awareness here. I think you can select to capture a skill, but when you capture it there will be a lock on it in your skill list indicating that you cannot use it until you purchase that campaign. You should be able to see that before you cap, so just be careful.

3) A lot of "you-don't-know-what-you're-missing" stuff, like the once a month chest runs in Nightfall that gain you a minimum of 20k in a couple of hours to fund your activities for the week.

I'm sure others can come up with more, but those are the ones significant enough to come to mind immediately. You will still be fine without the other two campaigns. I wouldn't worry about it. But the others are worth it, if you enjoy GW at all.