It happens sometimes, I'm watching a music documentary for example about a rock band or any other purpose. And you know the guitarist that is talking, you know how he plays, you probably are fan, but at any moment he can say that he is influenced or inspired by another band or another guitar player. Okay, but sometimes, he's talking about a band that play another kind of music !
Any explanations about inspirations and/or influences ?
Yes, musicians (and artists in general) look frequently outside their fields of expertise and aesthetical preferences for inspiration, to challenge their own assumptions and acquired habits, to look for new ways, etc.
Along history there has been some major currents of cross cultural influences. Classical composers have always been inspired by popular music and incorporated popular melodies in their compositions. In the beginning of the XX century many European (particularly French) classical composers where interested and influenced by the new Jazz music coming from America. Some jazz currents have drunk heavily from the theoretical bases of classical music. Rock has been influenced by Jazz and vice-versa. Rock has been influenced by classical music (a lot, and not just progressive or symphonic rock). Both Jazz and rock have been influenced by different types of (the so called) "world" music.
Individual artists may search along these common paths or have their specific, some times idiosyncratic interests and sources of inspiration.
These cross influences may manifest themselves in a more or less obvious application of tools, techniques and aesthetical values. Take as an example the usage of the sitar and indian music influence in some songs of the Beatles and solo work of George Harrison. I don't mean that such work is not creative and original, but the presence of a "foreign" influence is rather evident.
Or the influence may be less obvious and more indirect. Again an example from the Beatles, according to Donovan, Paul McCartney wrote Blackbird while trying to learn some traditional folk fingerpicking. Yet, the technique used by Paul McCartney in this song is very personal, not equal to any fingerpicking pattern commonly used.
A couple of other points to add to joseem's answer (which I agree with) -
There's the simple question of the passing of time - by the time many musicians became successful, popular music had moved on a lot from what they may have been first listening to in their younger and more impressionable years. This is perhaps less of a factor now, as there has been (I believe) a slower pace of change in musical tastes over the last couple of decades, but a successful musician in the mid 80s would have been unlikely to be commercially viable producing the same music he perhaps grew up with in the early 70s.
On the other hand, these days, musical tastes tend to be broader in general than in the past; people aren't stuck getting their music knowledge from one magazine or radio station as might have been the case some years ago; It's getting rarer to meet anyone who is only into a single style of music.
Musicians often consciously ignore genres, seeing all music as 'just music' with no boundaries; having a level of musical knowledge often makes it easier to relate elements in one genre to aspects of another.
If the above is true, you might ask why musicians often do produce a number of songs (or albums) in a similar style; I would guess that it's sometimes more to do with the realities of presenting a predictable product to a well-defined market sector than a desire to keep producing the same music.
If, say, you are a rock guitar player and try to play stuff that another guitar player from a different genre plays, you will surely play them with your own style and feel (mainly because you are not trained to play that type of music). This is not a bad thing, though. The opposite.
So something that was jazzy for example will come out as rock with a jazzy feeling. Now putting elements of other kinds of music in your music makes it sound fresh and exotic. You don't actually play that music, you just incorporate it into yours and your influences define your music and make it sound unique.
