You have to wonder why. What was the last home console to kick ass there?

Well of course it is.
It's a first world country with a population that is a lot higher than both UK and Germany. Per capita though, PS4 is more popular in other countries.

Also, factor in population. The UK has about half of Japan’s population and will likely pass the Japanese numbers in the end - I think it’ll have longer legs there.

Japan likes portability. Sony chose to stop making portable gaming  devices. Therefore Sony cares a lot about Japan.

Wait, what? No, Sony doesn't care about Japan anymore.

Everyday something hits me all so cold

Find me sitting by myself

No excuses that I know

The Wii

On a side note and another perspective 

20 million USA

26 million Europe

5.4 million Japan

14.6 million rest of the world

Can you really blame Sony shifting their focus to Europe. Just look at their exclusivesite this year. They where mostly targeted and marketed in Europe. They tried in Japan with marketing Ni-Oh, Persona 5 and Nier Automata. 

and yet USA is 4 times as important as Japan for Sony and Europe (with a similar taste in gaming) is 5 times as important as Japan for Sony.

18.6% of PS1 sales came from Japan
14.7% of PS2 sales came from Japan
12% of PS3 sales came from Japan
8.3% of PS4 sales come from Japan

Japan IS getting more irrelevant each year. Though that doesn't mean that it is irrelevant at the moment,

Japan was always strongest single market in gaming (if we dont count Xbox) after US and after hole Europe, there is reason why people are comparing US, Europe and Japan sales.
Japan always had much bigger sales compared to any European country, so difrence betwine PS4 Japan numbers and Germany and UK number are actualy very low, for isntance PS3 sold more 4-4.5m consoles in Japan compared to UK, while with PS4 difrence is only 1m curently and that difrence can easily become smaller.
PS4 sales in Japan compared to rest of world PS4 sales are definitely lowest compared to previous Sony consoles, including PS3. PS3 Japan sales were around 12% of world wide PS3 sales, PS4 Japan sales are curently around 8% of world wide PS4 sales and that perceant can easily go even lower.

So yes, Japan is becoming less relevant for Sony, PS4 sales everywhere outside Japan are amazing and Sony know that Switch will own Japan in any case, so I think they are not worry at all about Japan market beacuse they know they will have great sale reagardles Japan market.

The Sony "base" love to change the rhetoric, when it doesn't suit them. Or move goals, anything to put Sony in a good light.

Japan was always important, a lot of global phenomenons have started there, or came from there. The PS4 isn't an American product or an English product, it's global brand that started and is based in Japan. So OF COURSE Japan is important for the PS4, no question about it.

No Japan means no games like Dragon Quest and possibly no JRPGs as well as a heavily reduced amount of games from Japanese developers which would impact appeal, one of the reasons X1 is getting destroyed is because of no success in that region and one of the reasons Switch is garnering a lot of support is because of success over there.