I can't really watch it at the moment, but I know on my first (2nd hand) road bike, I'd changed tyres a few times (although, likely all 'half decent' tyres) but then I bought some deeper dish carbon wheels (£200 I think) on and was SMASHING PB's after that.
I thought it was widely commented, buy a bike, then buy new wheels for it as manufacturers often put very average wheels on them.
**EDIT** Probably a discussion for the Road Bike thread I guess?
**EDIT2** Tbf, most places are listing tyres as the number one upgrade. I guess I never really look at them as 'an upgrade', you simply choose what's suitable. Eg, the tyres I'm on now are not fast, they're tough. I'll switch to faster tyres come summer.