I have a pretty good feeling that "professional bike thieves" are not as widespread as everyone is so keen to suggest... and I completely agree about stealing parts (especially wheels, since I see tons of bikes around campus with QR wheels and not even a cable to hold them).
and it's not that hardened steels are the be all and end all of metallurgy, it's that they are harder to cut than the tool steel that cheap locks are made of, and the higher end locks are made of pretty thick pieces of said hardened steel, making them take even longer to cut. Given enough time and determination, any lock can be cut off. It's a question of whether the time and effort is worth it (and at a rack with a few other bikes, a well-locked one isn't).
Pretty much any lock on the market can be cut with a cheap oxy-propane torch from home depot in about a minute... but I don't expect John Q. Randomopportunist to be walking around with a cutting torch... or a grinder. If a ring of "professional" thieves want my bike, they'll take it... whether it's from the bike rack, inside the breakroom at work, or out of my house. Locks exist to keep crackheads and opportunists from stealing your bike. Apparently, this is lost on people.