Some people may not be familiar with C macros, and an example could help grasp the problem you're talking about.
You could have pointed out all the things that are done in the C obfuscation code contests, to illustrate your point, but maybe this is silly. Also, you start your point from the spaghetti code hell that C macros let people fall into (I guess you where thinking about #ifdef conditionals), but I don't see how annotations could generate that problem. Imho, your point is flawed.
C macros are useful, and when not misleadingly used, very effective at abstracting things in order to get the important structures apparent. That is what annotations attempt to provide. Regarding PHP annotations, the problem here is that it's difficult and time consuming to parse a PHP script, whereas comments are an easy target. SensioLabs went the easy road, perhaps also in the hope that someday annotations would find their way in PHP, and people would just have to remove the comments around them to be compliant.
