If you build a strong RPI early, it's easier to have a strong RPI later only because the RPI doesn't forget what you did early in the season. The same goes for a team that had a poor performance early. If you do that, it's much tougher to get back up because the RPI won't just forget what you did.
As Yazoo just said, it would be wrong to just disregard non-conference play. If you did that, then UK would be a 4 or 5 seed.
Now I'll agree that what you do later in the season may need to carry more weight, but when discussing two teams, you can't just ignore it if they tore it up in non-conference play against quality competition.