Can you upgrade your xprintserver in case apple decided to update their AirPrint protocol? Do you own the professional or home version of the server?
Yes, it can be upgraded - it has a fairly slick web-based admin interface, and it sends out the proper advertisements to make itself show up as "xprintserver.local" on the local network; log into it with your browser, and you can see current status, tweak printserver settings for printers, look at print queues and log files, and do various admin tasks, including telling it to go check for firmware updates. It's fairly painless to upgrade, and it automatically updated the first time I plugged it in. There have been numerous updates released, though I think they were all before I got mine - I was waiting for the release of the home version, since a) I don't need to run more than 2 networked printers, b) the USB port might come in handy at some point, and c) it was $50ish cheaper than the pro version (which has no USB and no limit on networked printers).
So, this part is conjecture, but I'm fairly certain the hardware between the two is nearly the same, aside from the USB port (maybe the pro model has more RAM, but otherwise they both have to perform all the same tasks) - I think they were initially targeting businesses where people were bringing in their own iPads (a $150 plug-in solution to get the VP's iPad painlessly working with the company's printers is a bargain for the IT department), but found an unexpectedly large potential market of home users who were interested, but put off by the price (a home user with a single inkjet printer can buy a nice new AirPrint-capable replacement for that $150). So they added a USB port (brings in more home users, but less prevalent in corporate settings - and the circuitry may have already been in the chipset, meaning just adding the connector), put in an artificial limit of 2 networked printers (to steer businesses towards the original "pro" version), and released it as the more affordable (i.e. somewhat less sticker shock) "home" version.
Anyway, one could make a good argument that I could have saved a chunk of money if I'd been willing to wake up my MBP on the occasions I needed to print from iOS, but it was/is such a nice solution to the "I want iOS to magically be able to print to my existing printer" problem that I felt it was worth it the cost - pay upfront to avoid many repetitions of a small inconvenience later.