The broader view is that it would be their 4th appearance in 8 years. Some people thought that was too much for Evergrey, and likewise Symphony X. Especially in a year that already has so many returning bands.
And we all know what happened last year when they played (though I don't think Jorn helped matters). There's a combination of issues:
1) They've played a bunch of PPs already
2) They've toured the area since then.
3) They likely WILL do a US tour once the new album is out.
I don't particularly like SX (seems I'm the only one). There are, however, a number of other bands I'd love to see return for that closing spot IF we had to have a returning band. The thing is, I'm not going to start thread upon thread saying we should have so and so return. Even if points 2 & 3 aren't an issue so it's my only chance. I don't want a returning band in that spot. I want a band I haven't seen and likely won't have a chance to see w/o PP. If they do a US tour on top of their PP appearance, so be it. If they come to my area after PP and I liked their set enough, I might go to another show.
You've got a band like Within Temptation that has finally made a deal with a US label. Of course, we'll get all the "wah! I don't like women in metal" people but they're still a perfect candidate with quite a following and a new album coming in 2007. Or you've got André Matos with a new solo album. I'm not an Angra fan but I did love the first Shaaman album. There's plenty off oddball bands that could headline the fest and many that I would love to see.
I think if we're going to have a band return that has played a few times in the US and hasn't played PP in awhile, I'd MUCH rather have someone like Jag Panzer.