I am also in the camp that an ideal surround sound room would have timber matched rear speakers, however, if budget or space is a concern, the rear speakers could be substituted with little sacrifice to the enjoyment of movie sound tracks. My impression is that you would be hard pressed to differentiate discrete sounds as being different from the front and the rear. What might be more noticeable are panning sounds from the front to the rear. The visual stimulation of movies makes the sound less critical in my opinion.
I am putting together 3 high quality timber matches speakers across the front and will use in-wall speakers for the side and rear speakers in my home theater. I mostly listen to 2-channel music so it is a good trade off for me. If I listened to multi-channel music, I might reconsider my choice of rear speakers.
Speakers produce sound regardless of the source (music or movies) and, therefore, the better the speakers, the better the sound noting that some speakers are not necessarily suited to movie sound tracks due to excursion limits, etc.
Cheers,
Tom