Right, but that's not the problem. The problem is that they are in fact still asking God to give them something. Something that is arguably even more desirable than material goods.
I don't think praying for selfish gain is the problem here. The problem is people's arrogance in thinking that of all the millions of prayers made each day, a divine ruler will place any importance on answering theirs.
It's like when at award ceremonies you see people thanking God for their success. It's this that REALLY offends - as if God is helping anyone win awards when children are starving to death every day.
Ultimately though, people can pray for whatever they want, selfish or otherwise. And if someone is praying selfishly, that's really a wider issue regarding that person's personality that needs to be delt with. No harm will ever come from the act of praying selfishly, as prayers can never be answered because God doesn't exist.