Okay Hyman, let's dissect it:
"All rights under 17 USC 106 are granted to you"
this is a grant of rights,
"for 1 (one) year"
this a scope-of-use limitation (only one year),
"provided that you purchase more than $100 of
http://shop.fsf.org/category/gnu-gear/ goodies in the previous year"
this is an act by which the grant comes into effect and from thereon
(for one year) you may enforce it against the offeror if it dares to sue
you for copyright infringement -- you will simply move the court to
dismiss the case with prejudice and award you attorney fees.
The above is a unilateral contract.