There have been several posts about why the past might not be a good indicator for NCAA selection right now; increased number of OOC games, parity in college basketball, and RPI tweaks that benefit non-BCS schools being the biggest changes over the past two seasons.
That said, your point on the RPI is correct, the RPI is rarely used for stand alone comparisons; ie. team A at 45 vs team B at 54 is not a comparison the committee uses. However, SOS, OOC SOS, conference strength, and quality wins which are results of the RPI are strongly considered. So as for the actual ranking, yes the RPI is not used much, but the secondary data that comes from the RPI is used bigtime along with how you finish and what you did on the road, etc.