False.This man speaks the truth.
Many enchantments have sweet spots where they are more common.
As aside I don't have issues with using books. I just keep my unwanted ones for use in Thaumcraft for there aspects.
Quit posting misleading statements.
http://www.minecraftwiki.net/wiki/File:Enchant_Probabilities_1.4.6.zip
Open Excel document. Go to "Pivot Table" tab, up top change to "Book".
Fortune III the sweet spot is LV 30. Pretty much all of the top-tier GOOD stuff on Books is only available at LV30 (other than Unbreaking, where you can do LV20). Silk Touch I is the exception, but if I have a decent spawn farm, I just do LV30 anyway since I'm enchanting 100 books and I'll get other good stuff.