You know, I don't really see much advantage for the consumer to the Blu-Ray disc format over the DVD disc format, even for HD movies. With proper, full utilization of the H.264 encoding format, most 1080P/24FPS movies should be able to fit on a DVD at a decent quality, 20-22 in Handbrake.
Of course, Blu-Ray has extra encryption. But that's
not a benefit to the consumer.
DVD-9 is not a big enough disc size for a 1080P HD movie format using h.264. At higher bitrates, you can cram a short video onto one using h.264, but that's it. Longer movies will suffer, and don't expect to get any extras. Also don't expect to have multiple high rez audio tracks either. That not only impacts on movie length, it also impacts on max bitrates for the discs. (Remember, the max bitrate for DVD is less than 10 Mbps, so to get decent bitrates, you'd need to be spinning at 4X or whatever.)
BTW, the above comments really only apply to H.264 and VC9. However, when it first launched, Blu-ray's authoring tools didn't even support H.264. The movies were pretty much all MPEG2, which required significantly higher bitrates. Furthermore, dual-layer Blu-ray wasn't available, so companies were putting MPEG2 titles onto 25 GB Blu-ray, but could use h.264 or VC9 for 30 GB HD DVD. Nowadays though, Blu-ray supports both dual-layer and h.264/VC9 so you get all the benefits. And now you even can have h.265 HEVC support with 4K Blu-ray discs.
Note that both HD DVD and eventually Blu-ray supported mastering onto DVD-5 and DVD-9, but that's only for very specific niche usage, not commercial movies. HD DVD also had the advantage of being able to do this at home, so you could put your home movies onto DVD for personal use, but people don't author 2 hour home movies. Also, the specs are different for BD5/9 than for Blu-ray. I believe the true max for Blu-ray BD5/9 is actually 30 Mbps. For Blu-ray BD25/50, it's 40 Mbps. I've read that effectively this means that for the video stream, you can only have about 24 Mbps on BD5/9.