thanks to the machinations of Chronos, there's no way that the entire Batman Beyond series could exist. when Green Lantern, Wonder Woman and Batman travel into the future in the JLU episode "The Once and Future Thing," to get ol' Chronos, we meet the new JLA (of a sort). however, since Batman has saved the day (imagine that) by causing Chronos to never travel to the future, he has effectively changed the events of Batman Beyond from happening.
which is good. I've only seen about three episodes of the show (not counting the ones in the JLU) and as Bruce himself stated, Terry was really just a Robin in a batsuit. bleah. and who wants to really think that nearly the entire JLU was obliterated in some untold disaster.
it's just one of any possible timelines stemming from various events happening in the animated DCU.
though it's still better than "The Batman"...