What exactly is an unfair advantage?

Game developers sometimes say things which come back to haunt them. Like Mark Jacobs defining the exact conditions for WAR being considered a failure, and then promptly fulfilling them. I believe that Mike O’Brien of ArenaNet just wrote such a thing that will come back to haunt ArenaNet when he defined their philosophy of microtransactions:

"Here’s our philosophy on microtransactions: We think players should have the opportunity to spend money on items that provide visual distinction and offer more ways to express themselves. They should also be able to spend money on account services and on time-saving convenience items. But it’s never OK for players to buy a game and not be able to enjoy what they paid for without additional purchases, and it’s never OK for players who spend money to have an unfair advantage over players who spend time."

Emphasis mine, because that is the part that will boomerang. The statement itself is one that a lot of people might be able to agree with. But those people will never agree what exactly constitutes an unfair advantage. And thus they will compare the reality of what exactly Guild Wars 2 sells by microtransactions with their personal definition of "unfair advantage", and pronounce ArenaNet to be in breach of promise.

That starts with things we already know about. Guild Wars 2 will have a system which resembles EVE Online's PLEX system: You will be able to exchange real money for gems, and trade those gems for in-game gold. Thus you can buy in-game gold. With which you can buy gear. Or in WoW terms: You will be able to buy "epics" for real money (as, btw., you can in WoW). Probably not the best-in-slot ones, but nevertheless. Any gear that is tradable will also be buy-able for real money. And a lot of people will consider that to be an unfair advantage of somebody spending money over somebody spending time.

The very principle of microtransactions is that anything which isn't pure fluff is going to save you time. You exchange money for time, and ArenaNet clearly says they want to sell "time-saving convenience items". But where exactly does "time-saving convenience" stop and "unfair advantage" begin? Lots of games for example sell items that give you a buff for a certain time that doubles your experience; is that a "time-saving convenience" or is that an "unfair advantage"? We will never get everybody to agree on questions like these. Some people will think being able to buy faster advancement and better gear to be perfectly acceptable, others will think it totally unfair that somebody can get to the same result as he did in less time by spending money.