Are you sure someone hasn't got it confused with the confirmed start of SFO-SEA and LAX-SEA on Virgin America, commencing March 18th 2008 ?
I can't see any sense whatsoever in VS going for LHR-SEA.
Until last year, BA (LHR) and SK (CPH) were the only european carriers in SEA.
This year there is BA, SK, AF (CDG), LH (FRA) and from June '08, Northwest commence non-stop from LHR.
That's a mega huge capacity increase even without VS gatecrashing the party, and yields can only deteriorate with the extra competition.
Stoney