For another thing, whether or not circumstance bonuses actually apply to the character's check or the task's DC is ultimately up the GM. Though the section on circumstance modifiers is small in the core book, it does mention this.
So sometimes its less 'having this bonus makes you better at the task' and more 'the task is easier because of this bonus, regardless of your efforts.'
Remember team checks count as circumstance bonuses, as those can be especially useful when a task might be difficult even for the character best suited to the task by himself.
Batman's Investigation bonus is at PL caps (+22), but Robin can auto-succeed on a Team check (cause its DC 10 and he has +15 Investigation), and with Teamwork, give Batman that +5 check, for a total of +27. Granted, this might be an example of one where a bonus is not truly needed all that much, but you better believe Robin would still roll to help Batman.