Misleading Article... Not 100% Flash (Score 4, Informative)

Yes everyone has flash, but what they don't tell you is that you'll also need the Swarmcast NexDef browser plug-in.
Check out the not so great review of the flash/nexdef experience: MLB Support Forums

Oh and if you want to also understand this from Microsoft's perspective: Miscosoft SL Team Blog
The CBS March Madness HQ streaming was SilverLight and was a huge success.