It wasn't "Volvo Spec". While your manual may say 5W-30 recommended (given the spec oil wasn't available in the US initially), Volvo Spec has been VCC RBS0-2AE/SAE 0W-20 from inception on all SPA cars. It could be found through a few sources originally in the US - there's LiquiMoly, Ravensol, Total, and Castrol that I've seen. If you read further in your manual it even says for Extreme Engine Operation to use Volvo Spec 0W-20. Why wouldn't you want to use the oil the engine was designed too especially in extreme conditions? There's a really good discussion that Billlk9989 pointed you to that yields the same conclusion.They'll pry 5W-30 out of my cold dead hands. It used to be volvo spec, for me it shall continue to be volvo spec.
Is volvo trying to save the whales or amazon rain forest with this move? Who knows. But out here in TX it's 110F in the shade during the summer and I want a nice thick oil since it soon breaks down anyway.