Regarding switching brands -- I would say that while it may be cost prohibitive, it isn't totally impossible. I am seeing a number of my Oly friends selling off and moving to Sony or Nikon these days with their recent product focus on m4/3 and out of the DSLR market as not everyone sees the e-5 as their next camera.
So long as one can afford it, there is nothing really stopping one moving to another brand -- even with an investment in present equipment. The way this stuff is changing these days, who knows what we'll be shooting with in 10 years? I am hoping to see Hasselblad come down to an affordable level by then. Who knows what the future holds indeed??
Of course, if you can include in your criteria the notion of growing your kit over time, then the idea of buying into a system as a newbie does make good sense.