As I recall, on close inspection of Audio DVD Creator's output (over a year ago, to be fair, in the process of writing my own app
Lplex, which is truly gapless & lossless) it appeared that Audio DVD Creator actually snips off the tail-end of each input file so as to align the audio data to the preceding audio frame on the dvd, then starts the next track at the beginning of the following video frame, so that not only was there usually a tiny data loss but also a playback gap if the relevant audio and video frames didn't happen to coincide perfectly. The gap duration is at most just under one video frame (NTSC = 0.033 and PAL = 0.04 seconds), so it's likely not always apparent to the listener. If the gaps seem longer, then it may have to do with your player and not Audio DVD Creator.
EDIT: The above applies to dvd-v compliant audio. If you're using CD-Audio as input the gaps may be an upsampling artifact.