I do find it a little odd/interesting that this capability was present in SH3 (where making it back to base was often one of the hardest parts of the patrols - a nail-biting experience requiring your boat to run a gauntlet of enemy air and surface forces that I always wanted to do despite the availability of this feature), yet it's missing in SH4 where, execpt perhaps for the Asiatic Fleet boats in the early war months, there really wasn't much in the way of suspense or danger on the homeward leg of the trip (certainly not much chance of encountering enemy air or surface forces during the run home from Midway to Pearl, after the first 6 months of the war or so).
I only used the feature once in SH3 - when (while using the LRT mod) I had struggled for a couple of days to get my boat back to St. Nazaire after being bombed just outside the Bay of Biscay, only to run out of time and compressed air about 100 miles west of port. I had managed to surface and close on two French freighters that were sailing nearby right at the end, and I felt justified in "warping" back to port on that occasion, on the theory that I was able via radio and signal lamp to convince one of the French merchant captains that he would not like what would happen to his crew's families back in Bordeaux when word got back to Onkel Karl that he had failed to stop and bring back one of his gallant U-boat crews and the U-bootwaffe's leading scoring ace
I suppose this may be a case of "be careful what you ask for" - perhaps the devs listened to some of the realism junkies around here and got rid of this in SH4
I consider myself a realism junkie too, but in my view there's nothing wrong with "unrealistic" features or capabilities like this one,
as long as you can turn it off or just choose not to use it if you don't want to - I hate to see any choices like this disappear, especially when it was already in SH3 and therefore would seem to be a relatively easy thing to bring over into SH4. Plus, I think the US boats were a lot more likely to be able to count on being picked up/rescued/towed back etc. (as long as they weren't still deep in actively enemy waters) than the German boats were, so this feature would seem to be a lot more realistic in the SH4 context than it would have been in SH3.
Would be nice if this could be modded - I was thinking maybe you could tinker with the saved game files a bit to "fool" the game into thinking you'd made it back to port, but looking at an "at sea" saved game and comparing it to the auto-saved "in port" saved game didn't shed any light on this for me as the files look radically different in those two types of folders. Maybe some real modding guru could take a look at this and figure something out.