There is some inconsistency about host sites. Last year, Colorado was the 10 seed, but the Buffs were sent on the road because their facility is inadequate. (It's mostly grass seating, not to mention it's cold there in November!) It's pretty obvious that we hosted Duke since we fill more seats, but there's more to it than that. There were simply too many tourney teams in Texas to send them all elsewhere (since there were no seeded teams in the state).
Auburn is hosting this year since there are too many teams in the SE, and too many seeded teams on the West Coast (such as Washington). The first two rounds are done regionally, but some seeds have to travel to reduce overall travel and costs.
The third round doesn't always make sense either. In 2002, 3rd-seeded Pepperdine traveled to unseeded Michigan in the third round. (The Waves ended up losing that match in the freezing cold.) The Aggies were at UCLA the same weekend. A friend took me out to Malibu while I was out there to see that epic match, and I can verify that Pepperdine's facility was quite adequate.
In 2003, Kansas was seeded #13. It was rumored that A&M would host Kansas in the quarterfinals because their facility is "inadequate". (I believe there was chatter about that on this message board in fact.) It turned out that the Aggies lost at Penn State, and Kansas lost at UCLA, so it was a moot point.
It's pretty rotten that Kansas got the edge in the seeding (8 vs. 9) if hosting is on the line. Yes, Kansas defeated us...in College Station. And yes, Kansas has allowed very few goals this season. But the A&M's schedule is considerably tougher...3 of the Aggies' 5 losses are to teams ranked in the top 15. The only team Kansas played in the top 15 is A&M!