IBM's Mainframe Monopoly?

So a few posts in the ZDNet forum commented that IBM is to Mainframes as MS is to Operating Systems. I dunno that I completely agree with the assessment. I say this mainly because it wasn't always Big Blue with 90% in the mainframe market. Unisys, Hitachi, even to a lesser extent HP were all in the game, but when the hard times came, the smaller companies took their marbles and went to the smaller playground. IBM toughed it out and while it certainly lost units, it retained a good % of the mainframe market. Since the Mainframe market is one part of a larger IT infrastructure (which could and has invariably moved away from Mainframes into mostly Server and Server Clusters) I think it's harder to call their percentages monopolistic. If you take it to a broader server/mainframe view IBM is probably at a loss due to mediocre penetration in the SMB category and pressure from vendors like Dell and HP.

IBM's recent suit against PSI is specifically a patent infringement case and licensing issues. Now whether or not this is just a tactic to keep PSI tied up for years in court is conjecture. I am curious to see just how another manufacturer could break into the market. Most of the big-giants are all but cold. Truth be known I think other than NEC and Cray I don't think there's anybody else that comes to mind for mainframes.