Largest banknote in UK is £50, largest in EU is €500. That does not imply a staggering difference in purchasing power between £ and €.

I wasn't particurarly supporting the argument that it is a foolproof way to measure buying power. Just that the decisions central banks make about their currency denominations aren't arbitrary and they do lend insight into the economies that they manage. The €500 probably isn't about buying power but it does tell something about the motivations for easing a transition to the Euro. In fact, now that the transition has been completed, the bill is being phased out. I wouldn't be surprised if that was the plan from the beginning.

Things in the UK are a little more complicated with their multiple central banks, but the £100 note is still being printed and while uncommon, it is in circulation throughout the UK.

Some £100 notes are circulated by some Scottish and Northern Irish banks (which are allowed to print their own currency), but given how rare the £50 note is, I'd expect the £100s be very rare even locally, and almost non-existent anywhere in England.

They almost certainly wouldn't be accepted anywhere except banks (many shops are suspicious of even low value non-standard notes), so I don't know if you can really call that "in circulation throughout the UK".

In the UK there are £100 notes, except they're only issued by a couple of banks. Here is an example:

http://www.worldbanknotescoins.com/2012/02/the-royal-bank-of...

I still remember the first time I got paid with cash, and received a couple of £100 notes. Most money I'd physically held in my hands up until then.

I guess what the OP meant was that the difference in what the highest note can buy is staggering.

Which is meaningless

It's just an observation that someone finds mildly interesting. Attaching "meaning" to it, on the other hand, is meaningless.

I don't see how that makes the argument of the grandgrandparent post. If some thought had been put into the denominations then what you'd assume to be normalized is purchasing power (since the smallest denominations should correspond to "a fraction of the cheapest thing I could buy" [if we include change] and the biggest should correspond to "more money than is reasonable to carry around for buying stuff"). Following that logic and combining it with yours the conclusion is "100$ in the US has similar purchase power to 15$ in India" or "things are cheaper in India", which really doesn't say much to me.