? 5W-30 instead of 5W-40 ?

I found that the VW dealer put in 5w-30 instead of 5w-40 today at my third oil change. I told him the manual says the oil must be 5w-40, but he was unconcerned.

The receipt says he used Castrol SLX Professional OE 5W-30. I bought a quart of the same from that dealer, and the container says: API Service SL/CF; VW

I'm sure that's very high spec oil, but what about the high ambient temp such as the high 90s that I'm driving in daily now? Isn't that what the *40* is for? Should I be concerned?

Thanks,

Roy