In regards to the plagiarism......I just can't help thinking "meh."
Ripped off, yeah, probably, but Led Zep was essentially just a folk/blues band cranked all the way up. And it's not like the blues are known for being original. Just say "got me a woman" with some minor variation 3 times in a row, then some other line regarding prison, death, booze, or more women.

I don't really doubt Led Zep ripped off those songs, but it's probably for the best. The artists they supposedly ripped off are a lot more obscure (well, to me anyway), and if they hadn't ripped 'em off, we'd probably never know they existed.