I think the biggest issue here, at least from the posts I've seen, is that most people do not seem to realize that hard disks are designed to run on average for a pre-defined number of hours before failure. Every drive manufacturer does this - they have to so that the mechanical designers can determine how robust (and therefore costly) the mechanism will be. Part of the determination of the time to failure is the duty cycle - or how much the device runs over a given period of time.
Most IDE drives are designed for a 60% duty cycle - or around 432 hours per month. For this series of drive IBMs is a little lower at about 46% - or 333 hours per month. Wheras SCSI drives are designed to run at 100% duty cycle - or 24/7 at even higher RPMs - which is one of the reasons they are more expensive. This does not mean your drive will have a problem if you go over the design spec. Some drives last for many years. Others don't last 5 minutes. But it will last less time if run constantly - its not really any different than putting miles on your car.
As well, IBM still honors the warranty if you go over the recommended time just like all the other drive manufacturers - no problem.
I asked IBM why they had published this spec since no one else does, and I was told that more people are starting to use IDE drives in servers in place of SCSI. The person I was talking to said that the biggest area of failure of the 60GB drives was in servers - I don't know if that is true or not, I'm repeating what I was told. So they thought it would be a good idea to let people know what the design spec is so they do not have premature failures in their servers.
I also asked why the spec was being removed, and the answer to that was with all of the press this is receiving, it makes it appear that every manufacturers drives other than IBMs are made to run 24/7, which is not true. Although with the cat being out of the bag as AmbitiousLemon says, the PR damage is already done.