SF emails

Thanks to eveyone who's written in on the matter of SF vs sci fi. It seems that the inclination - or prejudice - I picked up from somewhere years and years ago is shared. Dave F in South Africa:

As a hardcore science fiction fan for more than 40 years, I can attest that no self-respecting SF writer, fan or reader refers to sci fi, which I think is a media word given currency by non-fans.

Chris Smith in Shetland:

What you said! Other issues apart, SF is necessary for Kingsley Amis's epigram:

'SF's no good!' they bellow till we're deaf;
And if it's good? Why then, it's not SF.

Alan Brain from Aus:

For those who are wondering why,
What we call SF ain't sci fi,
It's just there's a fine line
Between Robert Heinlein,
And 'Son of the Two Headed Fly'.

Ian Bertram, however, is pessimistic. He writes:

I use SF but I suspect the battle is lost.

What nobody has yet written in to explain is how or where this preference originates, or why we all care, those of us who do. Is there any reason to it?