I've found pressure to be important for other reasons than the pure 1:1 translation. If that was the only usage case then you could get away with 256 levels of pressure, draw a straight line with a 256 px brush over the distance of 256 pixels and have it be the max resolution you can achieve at the highest fidelity.
With more pressure I am free to get more usage out of custom pressure curves and oftentimes the additional pressure helpful because I am very heavy handed. 256 is perfectly usable, I imagine 64 is too, but it's no replacement for the traditional feeling until it gets up to 1024. At 2048 I am closest to feeling like I can simulate natural media, however important that may be. You can map a really light pressure curve when doing watercolors and be really effeminate about it, or switch to a really firm one when doing more blunt media. That's a novelty though, and I could totally get by on 64 as I hardly ever use a brush bigger than that for detail work in the first place because my digital work tends to lacks nuance.
I think the surface pro has 512. I have one of those in my house and it draws just fine but you can tell it is less sensitive when trying to emulate natural media.