There is nothing normal about HS2 speeds. It seems ridiculous to go so fast when it costs so much more and the actual time saving door-to-door is quite modest. If it is all about capacity then the maximum throughput in terms of trains per hour is achieved at speeds around 200kph. Above 250kph noise becomes very significant so noise mitigation measures are onerous and tunnels require expensive porous portals. NTV in Italy declined to take up an option for more AGVs and ordered 250kph Pendolinos instead. The Germans have also ordered ICE4 trains with a max speed of 230 or 250kph. I can foresee HS2 trains running at speeds well under 300kph. It's only 175km from London to Birmingham and even diesel trains could do the 160km from London to Leicester in an hour.
Not all high speed services in different countries are entirely comparable. The HS2 model is much more like the Shinkansen than the European systems, as it tries to create a separate rail network designed specifically for the role it'll be performing. Unlike Japan we're not using a different track gauge so through running onto the existing network is easy to implement.
On the continent there are a much wider variety of lines and possible linespeeds. The Italians started building Diretissima back in the 1930s, when speeds of 250km/h were considered in the way that we see 400km/h today. Those lines are good enough today that there will never really be a justification to replace them, even though the line geometry does limit them to less than the current standard of speed for new lines. There's no point ordering lots more trains designed for new high speed lines and standards if they'll spend most of their time on lines which are fast but not quite fast enough.
Germany has the Neubaustrecke model of new general-purpose mainlines connecting up regions of the country. The newer ones tend to be designed for the most up-to-date speeds but some of the slightly older ones are limited to less than 250km/h. As you have been saying, high speeds are only worthwhile for long stretches of non-stop running, but in Germany there aren't many lines which really suit this model. Remember that Germany's network inevitably has to be much less efficient than ours (or Japan's) because their cities are arranged in a grid, rather than roughly linearly like ours (either side of the Pennines). Their ICE4 trains are designed to replace ICE1 and ICE2 sets that rarely, if ever, travel above 250km/h because they spend their time on lines which don't really go much faster.
The closest equivalent to the Pendolino and ICE4 in the UK is the IEP, which will run on our own quasi-HSR lines of the GWML and the ECML. The IEP is not at all in conflict with the idea of HS2.
HS2 is timetabled to run at 330km/h, only 10km/h faster than the state-of-the-art services on the most modern HSR lines. 360km/h capability is required but will only be used to make up time if there are delays. While the extra 30km/h won't make an enormous difference to end-to-end journey times, it may be the difference between a single-train delay and a multi-train timetable clash.
