No, you need that 80k to argue that Groupon's proposed product would infringe your trademark.
US trademarks are only good for the line of business I'm in. If I were to publish a software product called Mustang, for example, Ford wouldn't be able to sue me for copyright infringement. My product shares a trademark with one of theirs, but it's in a different enough market that the two trademarks don't conflict with each other.
It sounds like Groupon's proposed product is point of sale hardware. That's different enough from a desktop window manager that Groupon can quite possibly get a lawyer to convince a jury that they're different businesses. Therefore GNOME Foundation has to pay a lawyer to stand up and argue the other side of the case.