Q:

Allow rep from ALL Stack-Exchanges sites to be considered for rep-required functions

For what it's worth - my question is absolutely NOT a duplicate of the 'hypocritical' one linked above.. though it is similar.  I wasn't asking WHY Rep is independent between SE sub-sites (it's perfectly obvious to me).  I was instead suggesting a way to take other rep into consideration, and the question was answered quickly and succinctly, stating that, in effect, my suggestion already exists.  
I understand the rep-required functionality to prevent poor quality comments and whatever else rep is used for.
That being said, it is VERY FRUSTRATING when I (and I imagine others) have something valuable to contribute, or an important, relevant question to ask, but am denied the ability to 'comment' because my rep is lacking on the particular Stack-Echange sub-site that I am using.   
I end up posting as an 'answer' instead (because I'm the rebellious type like that) and then I get in trouble (frowny face)
Might it be useful to somehow consider other Stack-Exchange sub-site rep when determining restrictions?  Perhaps an average across all enrolled sub-sites?  Or as a specific example, considering Server-Fault or Stack-Overflow rep for Super-User requirements?  (As it would seem unlikely to me that someone with a good SF/SO rep would offer a low-quality contribution in SU)
Yes I know the management of this could be tedious.. but perhaps it is something to ponder?  
I speak from experience.. petty hand-slapping infractions by self-righteous moderators for not 'following the rules' is the FASTEST WAY to alienate a user who is otherwise trying to offer legitimate help.

A:

Might it be useful to somehow consider other Stack-Exchange sub-site rep when determining restrictions?

It kind of is already. Once any of your accounts on the Stack* network reach 200 rep, the other accounts will receive an association bonus of 100 points, which is more than enough to clear the more tiresome new user restrictions.
Unfortunately those restrictions, annoying as they are, have to be here. It's kind of hard to explain until you've had a chance to look at the review queues, but people do a lot of crapping on the site for lack of a better term. And not even maliciously - just things like misusing the answer box for questions or commentary (cough), or having huge discussions in the comments, or spamming, or...
There's a lot of value in keeping the feature set restricted until someone has demonstrated that they know how the site works by reaching the lower reputation thresholds.

