I'd like to add that in many cases, HD audio is also hard to tell apart from a DD/DTS track. Although this of course depends almost completely on your audio gear, I believe there were articles in the usual audio rags about how it was hard to distinguish. Same thing applies for music ripped to FLAC vs high bitrate mp3/wma/aac.
This is an age old debate. Ripping started because disk space was limited. Then the typical argument became - disk space is cheap, why not keep in the best format possible, you can always down-encode later. But now we've reached a point where the encoders are really good and space is again becoming costly.
I've spent a LOT of time ensuring perfect rips, 720p vs 1080p etc, and in the end realized I watched the movie only once and spent far more time on ripping it :)