Almost true. The Pentax K has a much larger selection, and the 42mm screw mount universe is probably even larger.
Originally Posted by JLP
Pentax K lenses were made by Pentax, Ricoh and a large number of third-party lens makers. The 42mm screw-mount lenses were made by Japanese and German makers, giving you a huge selection from which to choose. A K mount camera offers tremendous flexibility, by being able to take K-mount lenses and 42mm screw-mount lenses via an adapter.
But I agree that Nikon has done a good job at backward compatibility, unlike other makers, notably Canon.