include files (standard libraries) having a grey moment

I've forgotten how this works.
In 1.0.1 the [libraries] folder has [Ethernet] included.
In 1.5.2 the [libraries] does not have [Ethernet]
but in 1.5.2 it APPEARS to me that the previous version's [libraries] folder has been moved to the [hardware-arduino-avr-] and same for [-sam-]
Is this line of thought correct ?
Has compiler libraries localities changed between the 2 versions ?

Maybe I'm having a grey moment ...............

Yes, in 1.5.2, the locations for core libraries has changed. The reason has to do with trying to support multiple, quite different, chips with the same tool chain.

Much appreciated