They obviously did not count on Mike and others taking a close interest in their product. I suspect the relatively 'open' firmware writing style is replicated across many of their new products.
They figure that there are going to be very, very few people willing to take apart and fiddle with such a device, not only because of its price, but because of warranty and their usual customer demographic (i.e. people who don't know anything about how embedded systems work, but are "experts" at using TICs).
They could lock down the firmware even more, but that would probably just stifle sales back to their old value (and at extra cost to them to implement these changes), or even lock down the sensor somehow (and probably at even more cost to them) -- in any case, using the raw sensor directly is likely not above Mike's capabilities...
There are also a lot of other issues like their manufacturing process, QA, calibration etc. that come into it as well - the cost of making software changes increases sunstantially as a product moves from development to production.
Although not many people would be willing to open up a £800 product, if it is possible without opening, that changes, and bear in mind with the current software, you could decide to not make any changes to the internal files and just run it in service mode when high-res is needed, as it will stay there until the battery is taken out or it goes very flat - just putting it in sleep mode keeps it in service mode. The only thing you don't get that way is PiP mode.
There is clearly some very heavy profiteering in the 320x240 market segment at the moment, and relatively few players (many others are badged Fluke/Flir products). It only takes one to jump before the others all follow, but any comapnies that can't match the lower price for high res will be dead in the water.
However in the meantime, the low-end TIC market has to be very appealing as the volumes are potentially much higher when products get within reach for people who wouldn't normally consider buying a TIC, so if your product has a 'hidden' advantage over your competition then this has to be good for sales.
Of course there is also the fact that people love to get a bargain by subverting the system- the Rigol effect....
The question is whether Flir are sufficiently enligtened to realise it. Time will tell.
Something else I wonder about is whether suppliers of sensors maybe have some dodgy agreements in place to supply at reduced price conditional on the end products not being used at full res.