Deep Purple said:
And if the regular season championship is just as glorious, how come the postseason championship factors more largely into NCAA seeding?
This is debatable. For example, UH has a Top-10 RPI and won the AAC Tournament. The Committee picked Louisville to host a regional over Houston. Louisville swept Houston earlier in the season.
There are multiple factors here--including that Rice is already hosting one Houston regional. Two regionals in one city is not unprecedented, though. Several commentators noted that this was a sign that the committee still values the regular season over the post-season conference tournaments--Aaron Fitt of Baseball America tweeted something about this, as I recall.
That said/point made, addressing the main debate: I think this argument over which is more important is kind of silly. I think it depends. If a low seed came in and won everyone would say "no big deal, the big boys are saving their arms for the NCAA." You can even make a reasonable argument that OSU didn't try
that hard yesterday. In this situation though, which is actually unique, you had the top 2 seeds playing in the tournament championship game. Only 1 game separated the regular season records. They played before the 2-seed got on a turnaround hot streak of 27-3 in April and May, and they split the series (that the future 1-seed was
hosting) 2-1.... one of those wins coming very late in a game. The 2-seed had rocketed up the rankings and had higher RPI. Both were guaranteed to host a Regional and a lot of analysts expected the winner to get a national seed.
So, this Tournament was unique because you had the top 2 teams in the number 2 RPI conference playing for the first time in over two months. In a lot of ways it was a chance for each to prove how far they'd come in April/May.