This guy points out that japanese music may sound old fashioned to brits. Ì can't find the page now
but it's from wikipedia, about japanese music in general, where there's a reference to some work by some professor (If my memory serves me right). She points out that in japanses music of today you find a mesh of all styles that every appeared in music from 50s till today. An example of this is all singles of morning mususme, which in some years travels from disco through rock and dance and almost 60s like soft pop. It's also the biggest market for classical music (ever wondered why they picked these three styles:classical, trance and eurobeat, for ayu's remix albums? Obiously because they were the styles that could sell most at the time). The use of guitar solos has become rarer and rarer in western music since the 80's, during which is was as common here as there I think.
I hope that japanese musicians will never give up on this blend of styles to adapt to other countries music. That way I think it'll loose a lot of the creative points. The things he points at as reasons for "foreign" pop not hitting it in the UK are many of the reasons why j-pop blew me away when I first heard it, so although I don't mind japanese artists singing english and making it abroad, I hope they'll preserve the music.