Same with VFD as most other display technologies (such as EL or OLED, CCFL, ...)

Designs with high intensity will quickly burn down a significant amount of intensity.

Designs with more moderate intensity will be able to handle 5 or 10 times as long before the intensity loss will matter.

A big difference, when it comes to OLED, is that the first generation OLED from 2004 was very much worse than todays OLED. While a VFD or EL from 2004 had already reached the peak (?) of what the technology can manage.

A VFD is not so good for competing with incomming sunlight, because of the ageing. But with the lower intensity levels acceptable on a VCR, Microwave owen, ... it can manage lots of years will still look good. You don't notice the loss of intensity unless there are some display segments that isn't used normally, that you may wake up when entering like entering a setup menu.

With OLED, I think they are at the eigth generation right now, so lots have happened during the last 7 years. And all new design solutions haven't been aimed for the same problems.