Actually, I had to do that very recently. The difference between IBM and Ruby was I called in with my client's license information and within 20 minutes my IBM

Actually, I had to do that very recently. The difference between IBM and Ruby was I called in with my client's license information and within 20 minutes my IBM id had access to a WAS 6.x download. My client upgraded all their hardware (this was from old iSeries AIX to a new POWER setup) and had zero-downtime after completing the transition. The only difference was a significant increase in speed. WAS 6 still is being actively supported and hot-patched for security which is what my clients want. You're right though - moving up major releases can break things sometimes. I spent another couple of months forward-porting to Liberty so they could run 8.x but honestly most of the breaks I dealt with was dealing with third-party functionality that the old off-shore team decided to throw in. Regardless, during that period of time, my clients business was fully operational on that new hardware with a secure, seamless transition. I guess you sort of get the same 'future proofing' these days with VMware (the analog is basically: having old hardware, then buying new hardware and vMotioning your production instance to the new VMware ESX cluster), but you certainly didn't have that option 15 years ago, when my client was choosing what environment to run his oil/commodities firm. And that's just support on the hardware stack, rather than the 10+ year support that most businesses want as a guarantee.