They had the chance at $5 (even with a poison pill the buyout price would have been lower than now) and they didn't do it.
Frankly, I would hate to see a $60 buyout. I've done the math and know that a Rambus that is clear of the legal mess is worth far more than $60 stinkin bucks. We will own the DRAM industry, the graphics market, a chunk of the logic market and a whole lot more.
There's no question that IBM could make good use of the RMBS IP, but the two companies are outwardly opposite cultures with IBM emphasizing "open" system and Rambus clearly pushing the proprietary. I have it from someone at big blue that inwardly the blue company is tired of giving it away and they fight tooth and nail behind the scenes to cross license and collect their just due. But Big Blue does not see itself as an IP toll booth.