What's the deal with the invitations going out in the name of the Queen? Since when does the groom's mother host?
I believe that happened at the Wales and York weddings as well. I think it's a royal thing.
I doubt that a non-royal would be able to host a wedding in the style to which royals are accustomed.
ETA - not just from a financial standpoint. Influence and access to various state buildings would make a big difference too - I kinda doubt your average millionaire would be able to have a wedding at Westminster Abbey or St. Paul's.
The only people that can be married in Westminster Abbey are members of the Royal Family, Order of the Bath members and their children, and anyone living in the Abbey's Precincts.
As for St Paul's, only members of the Order of St Michael and St George, the Order of the British Empire, holders of the British Empire Medal, and members of the Imperial Society of Knights Bachelor and their children.