I totally concur. I used Roundwounds on my Fender-ish fretless for I don't know how many years and it does finally have grooves from string wear in the neck. I did take many many trips up and down the neck and many string changes later. But! It's a good thing, they're not like lava channels or something. And to tell you the truth, I think the more (or less flat) wear-grooved the fingerboard is - the better the growl. This is of course what Roundwounds are expected to do. If you don't want that sound and find some need for your bass to sound like someone humming through a comb and piece of paper, then I guess you can slap some flatties on there.
Also note that this is based on my Fender-ish bass, my Carvins and ESP basses - with ebony wood fingerboards on the necks. I do not own a Rickenbacker fretless bass.
That is a totally different story. All that 4001 using flats, and 4003 using rounds. But everyone puts rounds on their 4001's...sheesh. Like I said...another story.
SDG