1) I think the disparity has more to do with the change in granularity between editions. Skills go all the way up to a theoretical 13 in this edition, for example.
2) Personally, I feel the edges are easy to handle if you're the GM. First of all, just don't set any action on the edge where reasonable combat maneuvering can bring someone from inside to out or outside to in. Sometimes that's not possible... for example I ran a game where the runners were in the process of catching a murderer in the act of torturing his victim prior to the ritual killing. It was a published scenario but it didn't mention what the background count should BE much less how far throughout the building it might extend. I figured the background count would just extend to the outer walls of the building (which was a glorified warehouse). Of course, some PCs wanted to do things from outside the building INTO the building, which meant some were in the BG and some were out... and some actions (like a lightning bolt) were cast outside the BG into the BG. I figured a hard binary check satisfied my needs in running the scene: if the PC's physical/astral location or the PC's action involves the BG area, then the BG penalty applies.
3) Having lived (and even ran a SR campaign) in Fairbanks I've learned that the environmental effects of the cold environment are silly and not written with campaigning in Alaska in mind. Then again, the same is true for most RPGs, so Shadowrun is hardly the only offender game
But to be helpful and relevant to your point, I'd go with the simplest answer of saying for the purposes of your game, local natives have ways of avoiding that that are beyond the means for Runners from "the lower 48" to replicate or even understand. Of course if you're running a campaign in the Great White North, you'll probably have an easier time just House Ruling some tweak(s) to the rules as-is. For example, I house-ruled a hard cap of 12 hours on any not-bound spirit rather than allowing them to potentially stick around for months until the next sunup/sundown
4) See my #2. I decided that if you're outside the area but casting into the BG, it fully affects you. YMMV.
5) Can't comment much on 4e... I largely skipped that edition.
6) It effects EVERY Magic related check (although remember Drain rolls are not "checks"). Of course, keep in mind that ritual magic cast from an
aligned BG is gonna be fearsomely potent if all the participants are correctly aligned. Imagine how much easier it is for MIT&T undergrads who become aligned to the local background count there to use magic for their academic projects than it is once they get out into the professional world without those bonus free dice on tap all the time...