When you're inside a community (open source or otherwise), you don't see the barriers anymore, and you forgive them when you do. If you're a regular at a restaurant and the staff has one off-night, you can be patient because you know the food is worth the wait. If it's your first visit... not so much. And, importantly, you probably won't return. Initial impressions count, in software and in everything else.
One attribute of commercial releases is that major feature upgrades are announced with a lot of fanfare. That happens with open source applications that are household names (assuming an appropriately-geek household), but it's rare. Someone who tried your app three years ago and found it wanting may not realize that the version she can download today is far improved. Unless she goes out of her way to look, how likely is she to find out?
Perhaps you've gotten this far and decided my blog post is useless because it doesn't help you identify why your app is being rejected. Solving your individual problem is not my job. But there's nothing to keep you from asking those who download your app what they think about it. At its simplest, post a poll, asking users to rate the app (perhaps on different criteria). If you ask for an e-mail ID somewhere in the installation process, write to the downloader two weeks later to ask if they're still using it, and, if not, why not; you can also ask what they chose instead. This can be part of the committers' setting priorities: Is is more important to add that feature, or to improve app performance? Perhaps it's my own market research background, but it amazes me that people just don't ask.
But perhaps the reason people dumped your open source app isn't about the software itself.
CIOs and other corporate execs are often more concerned with security and support issues, but it isn't only the bosses who put the kibosh on FOSS adoption. Several responses touched on the desire for reliable support, or the fear that it wasn't available for the open source app. "I guess I wanted to ensure that I had a fully supported configuration with the least number of glitches," wrote one person. Vendors obviously take advantage of this fear in their sales presentations ("If I invite in a vendor, they will do a nice PowerPoint dog-and-pony show that I can't get from the open source community," one corporate user said, cynically) and in their own willingness to ensure support in one way or another. "The newsletter system we had often lead us reboot Apache, this way we opted by purchasing a paid webware instead, and since we have paid for the licence, we got faster support and they managed to keep us running without Apache issues anymore," wrote another user (a little cryptically, but I think the point comes across).