My lab (US Gov.) is the same, except there are is also no title change for the top level. I've been a 'Research Structural Engineer' for two years, and work with people who have been a 'Research Structural Engineer' for 40 years. They get paid a bit more, and have generally put in some time with a 'Group Leader' title, but they don't get saluted in the halls.

The consensus is that this promotes a more egalitarian culture, and prevents people from being locked in to roles they don't prefer. Senior staff are free to spend a few years managing a large project or in a leadership role, then back off to get back into the research.

There are 'promotions', but they're basically entirely disconnected from day-to-day work. I'm a 2; the lead is a 4, my boss is a 6 (all in the technical track). There's a separate management track, which has very similar salaries to technical ones (maybe 10-15% higher), which leave you with plenty of time to do technical tasks (management tasks account for 10-50% of a person's time, depending on the level of management), and I assume there is a tier where they don't disclose the salary structure for "executives" (major organizational leads). I'll get promoted to a 3 at some point in the next year or two; then I'll be a 3 for a really long time (with annual raises), and eventually get bumped to a 4.

Are regular promotions that important? As long as I get keep getting to do interesting work and keep getting reasonable raises I'm quite happy with my job title not changing more than once a decade.