[Elecraft] Curious -- why is KXFL3 roofing filter an option on KX3 ?

[Phil Hystad]

I have a curiosity question.  Why is the KXFL3 roofing filter an option on the KX3?  I mean, why is it not a built-in feature of the KX3?  First, I already own a KX3 with the KXFL3 filter so I am not asking this in order to choose to buy or not.  Caveat:  I am also a neophyte (philistine, ignorant, or troglodyte) in this sort of radio technology and still in learner mode.

But, it seems to me that the KXFL3 roofing filter is almost required with a radio as nice as the KX3.  Without it, as I understand the function, any crowded band interval like a pileup or close-in CW signals and such would render a KX3 (without the roofing filter) with less than the usual Elecraft stellar RX performance.

My guess, and this is only a wild guess, is that maybe the option leads this space open to future improved roofing filters?  Or, maybe even leave it open to a 3rd party market supplied filter (although, I think this filter is particularly different from other typical 3rd party filters).

73, phil, K7PEH