I see your logic but if you did a Best Band Of The 70s and The Jam weren't included it would be a travesty. Stats aren't everything - All Mod Cons only reached No. 6, The Gift got to No.1 but no one then, or now, believes The Gift was the better album.
I really don't think The Jam should be in this poll - their 2 best Albums All Mod Cons and Setting Sons were released in the 70s and the bulk of their hits were 70s tunes. In my mind they're the best British Band Of the 70s, which is why I've voted Tears For Fears here.