You're right, Steve, the field is indeed very narrow. But I believe part of the problem lies in HP's Esko Artwork DFE, which in my experience is absolutely horrendous. Their DeskPack "variable data" software is useless compared to competing software.
My biggest grip with HP is that you must use Esko's software to generate variable data - it fails to RIP anything created with other programs, so you cannot use 3rd party software. PDF processing speed is ludicrous, PPML fails right out (although the DFE uses PPML internally...?), submitting jobs more sophisticated than simple numbering slows the RIP to a crawl, and so on ad mortem.
After a year of suffering, we replaced the Esko with an HP Production Pro DFE. Now we use SmartStream Designer for regular VDP jobs, plus a custom built piece of software that I wrote to produce very complex jobs (output as PPML files).