You're confusing the Nortel and Novell bids. MSFT invited Google to join the group bidding on the Novell patents. The email I saw was an invitation to talk about joining, which Google refused, not a proposal of any specific terms.

Generally, it would be silly to expect Google to join a group and pay part of the bid, and not get a right to the patents, or have them encumbered. And at the same time, joining a group like this would by definition be cheaper than bidding against the group.

So, the only reason for Google to refuse to talk about joining the group to bid on the Novell patents would be if google was planning to use them against the group, if it won them.