It's not Apple's terms of use. It's how iOS binaries are created. On iOS all the libs must be statically linked. This means the LGPL code becomes the integral part of the app so all of the app must be released under LGPL. If you are fine with this you can have LGPL code in your app. This is one of the reasons if you want to use QT for iOS development you need to purchase commercial version.
It's well possible to statically link LGPL library and non-free proprietary code. You just have to provide end-users a way relink with their own builds of said LGPL library (i.e. give them an .a file with all your proprietary bits, and, if you're nice, a linker invocation command). Yes, this is some significant hassle to set up two-step linking (unless you don't really care about not revealing the internal structure - if you don't, you can just throw a bunch of .objs), but not a complete game-stopper.
Here what FSF says about this:
> If you statically link against an LGPL'd library, you must also provide your application in an object (not necessarily source) format, so that a user has the opportunity to modify the library and relink the application
