This is undoubtedly true. But I did find an exception to the general after-purchase retrofit. My first ST1300 was an '03 model, without ABS. In that first year, with ABS (a $1,500 option) you also got the adjustable windshield. No ABS, no adjustable windshield. I was able to rustle up the critical OEM parts to install the adjustable windshield for about $400. It took a bit of fiddling with the wiring harness to make it work, but it worked fine for years.Alex, I'll bet it would be $3-5,000 just to buy the parts. I remember the old thing about how if you built a car from parts bought individually it would be 20-30 times more expensive than it is.
Since the factory assembly-line premium for ABS was $1,000, it would probably be prohibitive.
Now this was something of an elegant "hack". Because the wiring harness itself is different with and without ABS (and adj. WS in this case). But it was a clean installation and served me well for years.
But ABS is a different animal, and I wouldn't attempt to hack it.