At the end of the day, SE's Abyssea sales webpage (and the description text in POL when you agree to terms to buy Abyssea) clearly states that level 30s can participate in Abyssea. Advertising that level 30s can enter and then increasing the level minimum after people have paid for the product (which we all have done) is a classic Bait and Switch. If they did that, they'd be legally exposed to truth-in-advertising lawsuits, not to mention I doubt it would take long for a breach-of-contract class action suit to form. And that's just in the US.

http://www.playonline.com/ff11us/addon/ex8/index.html

http://www.playonline.com/ff11us/addon/ex9/index.html

http://www.playonline.com/ff11us/addon/ex10/index.html

Game. Set. Match.