it is not uncommon for companies to cripple a device through the firmware.
In my experience (including ~5 years of CHDK development...), outright crippling is a lot less common than people think.
I feel the same is true for many canon point and shoot cameras, while not to the same extent but even with older models such as the sx230 hs, the limited control over the video shows that not all of the power of the SOC is being used (though not much work has been done of the video side of things with CHDK (eg compared to versions for older cameras, the current CHDK does not even allow you to lock focus on video, or manually adjust focus during video)
Limited *controls* are quite common. Not including video controls helps canon segment their market (pushing "serious" video people to their dedicated DV cams) and saves them development effort. Building a system with say, 2x more raw CPU power or memory bandwidth than it actually uses is not nearly so common.
If moroz suggestion that SX280 hardware was capable of 2x the advertised frame rate was correct, that would mean that Canon had substantially overspecced the parts. This would be rather silly when video frame rates and burst rates are significant point of market competition. If there was some other Digic 6 based model that had the capabilities, it would be a more sensible argument, but even that wouldn't be definitive, since other factors could still be at play.
(developing hardware is expensive which is why many companies tend to develop a single item and then find ways to cripple it and sell it for a lower price)
It does happen, but again in my experience less common than people think. Even if the CPU has more power than it needs, the low end parts will use slower RAM, bus speeds etc. There's also binning, where the "crippled" parts actually fail to meet the standards required for the high end products.
