I'm not sure about that (although if you're right, I apologise).
I think it's more likely that due to the fact that the Hairnets and 400's are on the same grid, that there was probably only a few spots left over for SV's and those that entered first, got the grid slots - there are reserves as well.
Same with Sound of Thunder.
There aren't many club meetings at Donny this year (3?), so people come to race as a one off - filling the grids and of course New Era would rather have their £130 than our (or anyone elses) £50 - and totally understandable.
New Era normally accept your entry and ask you to bring the extra £25 - it's happened to me before. That's why I don't think that is the reason.