VHols vs VS fare... too good to be true?

I have an upcoming business trip to the US, departing this friday, and I seem to have managed to not book any flights until the last minute. Company policy dictates PE only (I miss my last job! <cry>) and so I duly spoke to our TMC, who have informed me that the best price on a PE flight is ~ £2,300, for a non-flexible ticket! :0
I'm sure the company will pay it. I have to go, after all.
But, on a whim, I gave Virgin Hols a call, and - low and behold - for the exact same flights, and including a weekend's car hire (so I can nip to the beach and enjoy the Memorial Day weekend with some friends before work starts :w ), it's only £1,200 !

Am I missing something?

Is there some weird catch somewhere?

I know that V Hols have their own allocation of fare classes, and so on so forth - but the little voice in my head is saying there must be a catch somewhere...

For example, Does anyone know what happens if I need to change those VHols flights - unlikely for the outbound but possible for the inbound... do they permit that? What are the fees? Their website is annoyingly silent on the issue, and the lady I spoke to on the phone didn't seem to have a clue what I was talking about...

Now I'm wondering whether I can get away with upgrading to Upper instead

[Neil]

The VS fare, because the flight is so close now, will be an S or W, even if you search for cheapest these are what will come up, because the cheaper fare codes have advance purchase restrictions (usually 21 days), so that is why it will be expensive.

VH on the other hand must still have some of their H fares left which is why there is such a big price difference.

The VH one will be restricted with regards to changes and will have a fairly high change fee, plus you won't be able to upgrade with miles etc.