Joe,
In this thread, soilsample explains it well:
http://lawnsite.com/showthread.php?s...hlight=stamped
His point about fabricated decks in general being deeper and allowing more vacuum will, yes, in general give a better quality of cut b/c the vacuum causes the grass to stand up so it can be cut better.
And fabricated decks in general are stronger and more durable.
That being said, some Kubota owners here have said that their Kubuta stamped decks are made of heavy-gauge steel and have held up as well, and cut as well as any fabricated deck.
To me, the bottom line would be: don't let stamped or fabricated be your deciding factor.
Here's another thread:
http://lawnsite.com/showthread.php?s...388&perpage=10