Perhaps some rooms cannot accommodate 7.1 bed speakers. I didn't think my theater room could until I found a smaller width speaker that wouldn't block the doorway and got different furniture that let me squeeze another pair between the new rows (barely).
When I bought my previous receiver around 2006, there was 7.1 outputs on it, but nothing yet had 7.1 decoding support (that model didn't anyway). It did DTS-ES 6.1 discrete maximum and PLIIx 7.1 decoding. No TrueHD or DTS-HD Master recordings. A 6.1 layout made sense given the room limitations. Even though discrete 7.1 came out shortly thereafter (amidst the HD-DVD/BD war I chose to sit out with an Apple TV first gen with my mere 720p projector at the time), very few BDs actually supported 7.1 until Atmos came out (even fewer seemed to have discrete 6.1).
It's a small wonder Auro Technologies thought a 5.1 based height layout would be sufficient in 2010 given the unpopularity of 7.1 (even today I still see a lot comments suggesting they hear very little from the rear speakers and/or they'd prefer front wides to rear speakers. I certainly noticed very little from my rear center in 6.1 unless I used PLIIx and sat in the recliner that was behind them (it seemed to pull the sides into the back of the room by comparison instead of only in front of me). That may have been partially due to the "sounds like it's in front of you" psycho-acoustic effect of only using one rear center that sometimes occurs with some frequency sounds, although I found if I turned the speaker backwards or used a bipole, that no longer happened (former affected frequency response, though).
Rear effects are much more noticeable with many Atmos and X soundtracks for me these days, particularly with six (four bed and two overhead) speakers now behind my side surrounds and top middle speakers. There are also now three more chairs and two more rows to sit in than before so 6.1 beds weren't going to cut it any longer. But other rooms may not accommodate more and still I think 6.1 is preferable to 5.1 so I can imagine why he'd wan to keep it.