Such policy has been in place at least 2 years!
At one point the charge was a lot more than $10 - I think it is $15 or $16, when oil was at $140 last summer.
There are notice on the o....er, behind the desk, to inform customers of such charge if you cannot produce a receipt to show you have filled up the tank.
We always have receipt in hand and tell the lot attendant so. Never have been charged the fee. It used to be you have to do it at the counter, but I think they find a way to work around it and as long as the attendant is satisfied with your claim, he can override the system to get rid of the surcharge.
It is a fair practice unless you intend to scam the rental car company or the next customer.