This is a standard license for user generated content, and it's
upsetting to see people once again trying to stir the pot using it, as
they have before with almost every UGC site.
Note the following at the end of the paragraph on the license:
"...solely for the purposes of including your User Content in the Site
and Services" . Note that this is not an exclusive license either.
Companies *must* ensure they are granted a license to reproduce your
works, otherwise by displaying your uploaded works to other users they
open themselves up to liability.
Prusa is just being a troll, and makerbot don't deserve this sort of
trouble after the work they've put into the site.