I think the ones asking for a spec tire are requesting something that will last much longer then a 2 race weekend in FV.
The 6 tire program for F1600 & F2000 helps keeps costs down so your competitor isn't running stickers everytime they go out on the track over the weekend starting with qualifying. This is how this helps keep the costs down in the series but keep in mind this is really a semi pro series, meaning people spend more money overall to race here.
As pointed out much earlier, many FV drivers would be driving FF if they could afford the difference. I don't believe the people asking for a spec tire areafter the same spec tire as F1600 or F2000...Hoosier or GY would love it if this was the type of spec tire FV was looking for.