OMB - I know all that - so why sell regs on their own then? That sort of pee's all over your argument (all be it a sensible one) as any idiot can change a reg over (I've done it - with a fair bit of brute force).
You can buy car parts on their own - and it's the customers fault if they blow themselves up!
Then there's the bottles that are out of test (for whatever reason) - most people only bin the bottle - not the reg as well. I'm sure a lot of people would simply buy a new bottle rather than even pay for a new test in the first place (if they were cheap enough).
Which brings me nicely on to snipa's post. £100 for a bottle on it's own seems expensive when I can get a
'set up' one for a bit more. And
this one for only £40!
*shrug*