He sold 20 million+ of those American Songbook records and in my opinion they are among the finest interpretive collections of that music ever recorded.
Those records blow
and, like others have said, he wasted all that time singing crap that Michael Buble could sing 10X better while asleep, while his "rock voice" got weaker and weaker.
That clip up on YouTube of him at a Jeff Beck gig from 2 or 3 years back - Rod just doesn't have it anymore.
(The guy from Simply Red who was singing w/ Ronnie Wood and Ian MacLagan recently actually did a good job however).