Rik, you've hit the nail on the head.
I work exactly the same way.
The problem with deferments is that everyone in the industry knows deferment means "I will never get paid." it is exactly the same in the Uk as it is in LA and my guess is, it is the world over.
It's not an incentive and most pro crew would rather be told right off the bat "Guys, we're doing this one for love."
If you've a good script and a reputation for running a good shoot, where you're not wasting people's time, then people will come out to play.
The other danger of deferments is they pretty much always cause post completion resentment.
Even when an actor "knows" it's only a long shot that they'll see any money from the deferment -- when money is tight and the film isn't turning into the career breakthrough they wanted it to be, they'll bad mouth you all over town.
A producer's reputation can only survive that kind of flack for so long.
My ex business partner carried on making films after we split and never learned this lesson. He now has a dreadful reputation for making financial promises that don't pan out.
I, on the other hand, have had held onto my reputation, because I've always been completely up front with people about money.
There is no percentage in playing the "big shot" in this industry -- it's always better for your mouth to be smaller than your wallet, rather than visa-versa.
Ironically, in an industry that has a reputation for being full of B.S., it's always played to my advantage to be completely straight in all of my business dealing.