I can understand that perspective. There's always a personal and professional decision and tradeoff, ideally done in a conscious and informed manner, of specialization vs generalization.
My world is drastically different than the mean HN poster I think; but I'm fairly convinced that by number of people it employs, it may be the more common one. There's just a lot of boring but eternal business applications out there.
FWIW, I've been a "PeopleSoft person" for 25 years now. So from that perspective I'm specialized, but I would not call it a dead end. In that time I've also worked with Windows Linux AIX HP-UP; with DB2 on mainframe and unix, Oracle on Unix and Windows, even MS-SQL once. On premise, hosted, and now even cloudy. Done development, database administration, system administration, upgrades, performance testing and tuning, data disaster recovery, infrastructure architecture, etc. So I've led a wonderfully diverse, interesting, challenging and satisfying career - inside a very specific niche ecosystem :) . Around me are respected professionals with DEEP and profound understanding of that ecosystem, who do their job exceptionally well, consistently deliver client value, and most of us find our own kind of variety. None of us feel "exploited by the employer", for what it's worth (I have fair control of my career and direction), and are generally satisfied with our chosen lot in life.
I can see why that works for the employer but as an employee I would be terrified of that becoming a career dead end.