The problem with this on older consoles is most games are not built to run and output as they get it (most modern PC games) but run and set to output at a given speed (see also why PAL and NTSC versions of consoles might have subtly different clock speeds, also the whole thing with bad PAL conversions). Overclock it and you have a poor emulator style turbo button. That said in this case the video shows superfx things and where you might expect the clock to increase by 12% the difference from lack of sync at the start remained the same so it is closer to modern PC stuff there in the car game (I hope there is nothing more subtle going on), I have less easy ways to tell on the mech game (possibly fire rate of the main cannon) but it was not an obvious boost and you can usually tell for 12%.
If you are doing the old things you can improve code if the devs made questionable choices, you can set update rates sometimes for text in various ways, you can slice frames out of animations or boost the movement rates so it hits the completed position more quickly. Equally most PAL TVs have supported NTSC modes since... most you will still find working anyway so PAL users can boost their console and enjoy NTSC/as the original dev was satisfied to let get go out of the door frame rates. There are a few that cut the other way as well (games designed and programmed for PAL regions that saw speed up for NTSC) but let us not go there as you also have to deal with PAL resolutions being greater. I guess you can also mod the game for hacking purposes like FCandChill mentioned, on a stock game it is not going to do all that much.
Generally though if you see a lack of them then that is because the former is perhaps one of the harder things to do effectively, http://www.neocomputer.org/projects/et/
is probably the best example of it happening sans source code/source level remake. The others are far easier to do but they tend to be gameplay level slowdowns (the crawl in text crawl being the operative word sort of thing) than framerate issues. If you are a complete cowboy you can mess around with vblanks but for most that is a recipe for crashing.
If you reckon turbo button is acceptable (you can possibly go into the game and slow the audio so it matches back up after a fashion) then that could be done in hardware, the usual concerns about heat and longevity when it comes to overclocking also wanting to be considered.