Likewise Adam, I have no doubt you know what you're talking about, as do all the Aloha guys on here. In some cases, I think it's just a simple matter of what our experience is in. For example, my experience with Aloha QS is pretty limited. If someone asked me to come to their location to resolve a QS issue, I have no doubt that I could in 90% of cases. But, I am no where near as proficient compared to TS. That's just my market.
As it pertains to myself, I do not work for an Aloha dealer. That said, I see my fair share of clients that are still running 4.2x, 5.0x, 5.2x, etc. They may not want to upgrade their Aloha software--but as you mentioned--sometimes the server decides when it's time to upgrade the hardware, and not the customer.

As such, I agree it's a good idea to get them on a newer OS when the file server finally does die. And generally speaking, my experience has been the older the Aloha software, the less likely Aloha will see the security key when running on an XP platform. On newer systems (within the last year or two), this is never an issue. Not only that, the number of issues I see with Aloha on XP vs. 2k is a no brainer--2k, almost zero problems, solid as a rock.
Does this mean that it's impossible to get older versions of Aloha to run on XP? Absolutely not--in fact, I would probably agrue the opposite--that someone determined to get 4.2 running on XP, who really understood the architecture beyond that which is required by a good tech, could do it if they were willing to dedicate the time. But most clients don't care what OS is on the back, since they only use it for Aloha (and we strongly advise this, as I am sure most of you guys do too). They just want it to work without hassles--as do I.
A while back, I posted on Tek-tips, asking if there was some kind of guideline with respect to which version should be using which OS, and the response I got was more or less that others had seen issues too, but couldn't say for sure when you need to use XP or 2k. Don't get me wrong--I would much prefer to use XP, if for no other reason that it finds most of the basic drivers for you, it's more user friendly, and I find it to be stable. At the same time, I think customers and techs sometimes get too caught up on what's considered "old", when sometimes it's just about what's get the job done. When something gets too old, it is a problem--for example, many programs, like Anti-virus, won't run on NT 4.0 anymore. But I have yet to see much that will run on XP that won't also run on 2k.
I was more or less assuming that the genteman who made the post was likely looking for the easiest solution (unless he's a full time Aloha dude), and in my opinion, that would be 2k. There are no doubt a lot of factors involved--the way the OS is setup, the way the Aloha software is installed, the type of hardware, etc. So I am in no way proclaiming that my experience is "the way it is". Just what I've seen.