Basically, his key view of why time after time some very specific applications are given so much hype and attention, are delivered and then are left seemingly abandoned, is down to the ageof the developers. Matt clearly identifies that the developers of these apps as well as himself are constantly bombarded by the huge array of new technologies that are being made available to programmers and the many new and exciting ideas that accompany them. Being the young age of 19, its very hard to stay focused on just one project, especially if its not utilizing "cutting edge" technologies.
OK, so I'm not 19, I'm 21 in a few months but I can definitely relate to what Matt is getting at. I've always got a few projects that I'm working on and I'm always thinking of new ideas that would make great projects. Just as Matt recalled, I too can't count the number of projects that I've started and subsequently not finished because the next best thing comes along and I get distracted.
For example, Switch the backup utility that is listed on my projects page but has never had a single download listed is a prime example of one of my own forgotten applications. Switch was actually the first relatively large Cocoa app that I created after moving to the Mac as my primary platform and after learning the basics of Objective-C. It was to some extent the basis for me to further my learning, that was, to be hacking away at a specific project. Switch actually became bigger than I expected and I decided to continue developing it. But then, after months of development I got stuck and eventually bored and decided to take a break and start a new small project for a slight change of environment. This project eventually turned into the distraction to going back to developing Switch and ended up being SafariTabs, which unlike Siwtch is currently being actively developed and is appreciated by its many users. The key thing to note here is that I like many others became distracted over time and slowly abandoned the project, but as noted in the comments to Matt's post I'm becoming more responsible in my maturity and will soon be returning to developing Switch.
So I've said way more than I intended but I've finally vented my frustration of nearly never quite finishing anything thanks to Matt (that is venting my frustration not, not finishing anything), but his view and insight into the "Delicious Generation" never quite materialising or following through is definitely worth a read.