Can't really say why the tech department recommended the 10W-30 over the 0w-30, except I do know that they've added some folks recently.

In May, one of the vendors to AMSOIL made the comment that, in his opinion, there is no better oil available than the Series 2000 0W-30.
In all the bench testing, the 0W-30 comes out a bit better than the 10W-30.

When the 0w-30 first came out, my son-in-law helped himself to a load and replaced the 10W-30. He later called me and said he was consistently getting an extra 50 miles per tankful before the little red light came on.

Granted, both of these oils have had several reformulations in the past years, but I still feel the extra $10 a year is well worth it. Certainly nothing wrong with either the 5W-30 or the 10W-30. I have 2 shops which specialize in Volvo and Saab repairs. As the primary synthetic shop oil, one uses 5W-30 and the other 10W-30. The owners (and some of the techs) use 0W-30 in their own.