Ed, shortest answer: Don't use [expr] if your worried about this.
They don't like it, but we can still *technically* use LGPL code like [expr] by providing the object files, which are of course useless to anyone who hasn't jailbroken their device or paid the $100 iOS dev tithe. Lots of apps use LGPL libs.
This really all comes back to the fact that iOS apps must be statically linked and the distribution channel is controlled, which is why GPL code can't legally be used on the App Store.
Much of the discussion below was prompted by questions about using libraries with iOS and in particular compatibility with Apples stores. Apple hasn't allowed either GPL or LGPL software on their app stores, libPd avoided expr etc to conform with Apple's policies and hence be allowed on Apples app stores. Changing to LGPL won't change that, Apple does not like copyleft.
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Dan Wilcox
@danomatika