There are plenty of reasons why people use vacation. For those who propose to modify the rules to benefit themselves to suggest otherwise is absurd.
For example, it is a common fallacy to suggest that people who are "on vacation" should not have the right to come here to play live chess (really gets these rule modifier proponents up in arms!), or to browse in the forums. Is it really that hard to imagine that your game with this opponent is not at the center of the universe?
If you can only join one tournament, then simply join a no-vacation tournament. I am not sure what the fuss is about.
Gosh, why have a simple answer when you can instead have 4 pages of whining?
Of course, someone will pop in and say :"but it will take me a year to get out of my current tournament when I foolishly entered a vacation tournament", to which I respond "yeah, same here, I have this no vacation tournament I foolishly entered, will take me a year to be rid of it as well."
Next time, we both will read the fine print and think more carefully, yes?