Actually, the process for older forged clubs was a little different than todays forging. Older clubs were 'triple forged and triple chromed' with a layer of copper, nickel and chrome. The game back then had a softer ball (wound balata). Today's trend is just the opposite, harder ball (even though you have a softer cover) and a milder steel to give the same 'softer feel'. Production of older forged clubs was more labor intensive with more hand operations which have now been eliminated in favor of lower costs and production. All you have to do is look at some of the Macgregors, Wilsons, Hogans and Hagens from the early 60s to the 80s and you can see the difference. I have sets from the 60s, 70s and 80s and my regular gamers are 83 and 87 Wilsons that aren't even close to needing replacement.
On the other hand, I had a set of Cleveland TA3 Form Forged irons that were considerably worn after 4 seasons. They showed noticeably more wear than my 60's Wilson!
I will agree with some of the other posts though. Clean your irons regularly, particularly after each shot and during practice. If you are hitting balls with dirt and sand on the face, you are abrading the face of the club with each strike. You might as well take a sander to your clubs. There is a reason why caddies clean your clubs!