As far as I know Roundup is a general use herbicide. If it was only licensed for use with Monsanto's GM products then I think Monsanto would have a case - assuming there were equivalent non-Monsanto herbicides freely available. I doubt Monsanto would be pretty happy about that however.
UPDATE: There was supposed to be some form of "terminator" gene included in the GM products to explicitly prevent generation two seeds from being replanted. I guess since we are talking about law-suits that did not really work as expected.
I'm curious to know what you mean by 'equivalent non-Monsanto herbicides'. Roundup is specifically designed kill everything except Monsanto's GM crops. Are you saying that farmers with contaminated fields should be able to use a non-Monsanto herbicide which is specifically designed to avoid killing Monsanto's GM crops?
Glyphosphate (Roundup) is a now off-patent general herbicide that will pretty much kill everything (even your crop) unless it is genetically modified a la Monsanto's RoundUp ready crops. This is often how Monsanto finds people to sue; people that buy Roundup without buying the seeds.
UPDATE: There was supposed to be some form of "terminator" gene included in the GM products to explicitly prevent generation two seeds from being replanted. I guess since we are talking about law-suits that did not really work as expected.