I'm certainly not an expert in this area but I've dealt a little in drain systems.
I live in SE PA and around here, Soil Injection is not used. (Well, let me qualify that - I personally haven't heard of it being used.) But from what little I've read and heard about it, it's not that highly recommended. And when it is done, it's usually done when work on the interior (to fix the problem) is not feasible. IE., finished basement, small crawl, etc., etc..
In any event, here's a reference at Popular Mechanics that talks about it and other mitigating measures. If you still have more ?'s, post up.
I don't know that soil injection is 'illegal'. I guess you'd best get an answer from your local Municipality's Inspector's Office. As for the differences between SI and a 'tube system' is night and day. SI is a foundation coating and a 'tube system' is just, well, a tube system. (You can see the latter at the above link.)
I hope I answered your ?'s. My best to ya and hope this helps.