Yes, but if the price is rising people are going to hang onto them there's no large profit to be made in a £5K - £10K car.
Agreed (hadn't checked the Rovers TBH), and it doesn't help that the MGs are split into differently named entries, but I think the pattern still shows that cars are gradually disappearing into SORN at the same rate they're becoming unlicenced - so they're off road but not scrapped.
I suspect the SORN cars are being tucked away until they're worth more as we're past the bottom of the depreciation curve. There's a small fluctuation in SORNs between Summer and Winter as cars come out to play in the Summer, but the trend is a gradually increasing one.
Then you have owners who see the future appreciation for these cars and are trying to keep the miles off them and in the garage rather than using as dailies (although it's bloody hard!) with no intention of selling for as long as possible (that's me then).