I am completely with Oni and Tsyr.
I don't care if it's just one page, if you sell me something without telling me that I need to buy from you something else or I won't fully use your product, I have all the rights at least to get my money back if I want. But usually I don't want that, I do want to buy and use WotC's products, and I want them to be as good as they can be, without this sort of "leggeresse" by the authors. I haven't seen the BoED, but usually WotC books have a diciture on the introduction that says "You need PHB to use to use this product..." or whatever, and it should say "you need MMII to fully get advantage of this book" if that's so.
It is not a practical matter, it is indeed a matter of principles, like Frostmarrow says. Especially if it's one single thing (PrCl) that I can't use. Why did they have to print that PrCl that way if it wasn't so important? Furthermore, I bet that the PrCl is quoted in the WotC's site commercials about BoED; if that's also true, what if a kid decided to buy BoED because fascinated by the name or description of that PrCl? That's just a fraud.
On the other hand, I REALLY appreciate if they release some (I mean SOME not A LOAD OF) books which synergically use each other. For example, I have borrowed long ago the ELH and other books which have epic characters, but they dont's use epic rules. This obviously saddens the ones who bought ELH because it looks like the ELH is usable alone but not easily together with other books. But if you print a book that uses ELH then make it use it on a regular basis and write on the back cover "This books lets you further exploit the ELH in marvelous ways!" so that I know what I am buying.
Besides, they could always release web enhancement to exploit synergies instead of web enhancement that almost always simply give crunchy bits that you never get to know why they didn't make it to the printed book if they were worth.
Or otherwise, why not using the wonderful sidebars for variants? Make the PrCl by default summon a monster from the MM and let the sidebar give the variant of the Tempest if you own the MMII.