If you'd actually read the thread before posting, you'd know that Mike confirmed a good while back that the 650 design wasn't meant to provide simultaneous use of each tuner.
IMHO arguing whether this is a design flaw isn't a very interesting discussion but the question Octaven raised early on of exactly how the driver and higher level applications such as Media Center and BeyondTV will handle potential scheduling conflicts between attempts at simultaneous use of the tuners is, and to date hasn't been answered.