Can't say whether it's true, but the purported reason was stated in the article (same sorting used for declaration and for deallocation, to make reviewing for memory leaks easier).
> dealloc should process instance variables in the same order the @interface declares them, so it is easier for a reviewer to verify.
One engineers idea of 'logical order' may not be another's, so alphabetical order seems as good a sorting method as any. And since the article itself doesn't link to the style guide, here it is:
http://google-styleguide.googlecode.com/svn/trunk/objcguide....
Google keep it regularly updated, so it includes newer developments like ARC and the modern literal syntax.
(Also, line lengths merely have to 'try' to be less than 80 characters, so there's wiggle room here too.)
I don't see anything offhand in the internal ObjC guide about alphabetical order for ivars, so it's possible the OP misunderstood the "dealloc in declaration order" rule. It's also possible his specific project had a convention of sorting them alphabetically.
Personally I generally organize by kind: model (including state), and then interface (views, etc), and then controllers (including helpers).