I wouldn't read too much into this - Amazon's Ireland region was deployed earlier (2008?) than London (2016?) and seems to receive updates earlier too.

London only came online relatively recently, maybe there's some operational stuff getting in the way of deploying? Or perhaps London has relatively few users at the moment, so the number of clients who will be able to take advantage of more specialised instances is also relatively low?

Because Ireland is so close to the UK that the latency will not matter?

Ireland is one of the older and larger regions, and generally gets new stuff at the same time as Virginia or very shortly afterwards. London and Frankfurt tend to be delayed a bit. See https://aws.amazon.com/about-aws/global-infrastructure/regio...

The London Region is really new. Amazon are using it as a way in to UK-only projects (specifically healthcare due to NHS regulations). I suspect their datacentres are considerably smaller than that of Ireland along with their client-base for the moment. I wouldn't read too much in to it, brexit-wise.

London region is tiny and not the region to go to unless you have specific geolocation requirements.

The Dublin data center is probably much larger than the one in London, for starters.