>F.ex. when MS writes "Comparing Visual FoxPro to Other Programming Languages" they are wrong with their own product, or are they?

I'd say they are partially wrong. Assume you're comparing two portable radios - one of them has a CD player, and the other has a flashlight. You're comparing them as radios; that's the comparable part. Then you can go and compare how each benefits from the rest of the goodies they have, but you can't really compare those goodies.

So, if they're "Comparing Visual FoxPro as a programming language to Other Programming Languages", they aren't actually comparing the whole product to another product. They're comparing one aspect of it.

Besides, what's usually missing almost everywhere (except in the Hackers' Guide) is that Fox has several sublanguages - textmerge, data definition language, internal SQL sublanguage, low level file manipulation language. Did I forget any? When comparing Fox to other products, these usually get out of sight, don't know why.