It is vaguely similar, Spiderman's ass is not arched up like he's getting something stuffed up his butt. That he has to go back 10 years to find something comparable is proof enough that this pose is not very common for Mr. Spiderman.
If you are going to play that card maybe we need to examine Spiderwoman covers over the years.
http://www.coverbrowser.com/covers/spider-woman
4 out of 50 are of questionable taste and more importantly look like something you wouldn't see with a male character. There is a fifth one that also fits the second point but it isn't objectionable.
http://marvel.wikia.com/Spider-Woman_Vol_2
1 out of 4. Maybe 2.
http://marvel.wikia.com/Spider-Woman_Vol_3
0 out 18
http://marvel.wikia.com/Spider-Woman_Vol_4
1 out of 7 but it falls under the not a male pose but not objectionable material.
http://marvel.wikia.com/Spider-Woman_Vol_5
0 out of 1.
You have no credible argument.