I honestly do not know, I wasn't employed here when the forest was first stood up.
We can do the site links, but kind of like to keep those to a minimum when possible, we have over 100 AD sites. I guess our main inquiry here is why can't Exchange tell Outlook to use the GC sitting on their user's subnet since it would score a 28 vs 27 for a GC in Exchange's site? Why does the limitation of the Exchange site or a directly connected site built in when it isn't Exchange itself using the GC for these operations (or am I misunderstanding it?)?
I beleive my primary goal is going to be obtaining and deploying new GCs in the hub sites for each domain and modeling our Site links to look more like our DNS heirarchy configuration.
We just want to know "why" it is this way. :)
Thanks!