Your points are good ones. However, you and other make reference to "low bitrate MP3s". Isn't that somewhat besides the point? If you're going to compare Ogg Vorbis q6 or q8 to MP3, you should compare to the best and most widely available codec and encoding options.
By far, the most popular MP3 encoder is LAME, and the preferred format is V0 or V2. V0 generally has the most downloads on the popular private bittorrent trackers, but V2 is the choice of "scene" release groups.
Neither is low quality. V2 averages around 192 kbit/sec and V0 around 245 kbit/sec. There is very little perceptible difference between LAME at V0 v. 320.
While Ogg Vorbis using the aoTuv encoder can achieve transparency at a slightly lower bitrate, from my ABX tests, and reading on Hydrogenaudio, you save, at most around 5%.
I grant that this may be valuable on a DAP. While there are DAPs with Ogg Vorbis support, lets be honest here. What's the most popular DAC on the market? Apples iPod or Touch/iPhone, most likely. The vast majority of people I see with DAPs use an Apple product. Unless you use the third party Rockbox firmware, which substantially reduces the UI quality, one of the reasons people pay a premium for Apple products, you're not going to have Ogg Vorbis support.
So, while it is possible to buy a DAP that supports Ogg Vorbis, you have to make your hardware purchase based on your codec choice, which really shouldn't be the case.
You suggest that Ogg Vorbis support is only a problem if you're looking at cheap DACs. This clearly isn't the case. If you want to use an iPhone, Apple Touch, an iPod or any other popular DAC, you have two lossy choices - MP3 or AAC.
So, while you do gain some space by using Ogg Vorbis, IMHO it's not worth the limitations in hardware and software choice.
As for desktop usage, conventional hard drive storage is so cheap, that it is really inexpensive to simply rip to FLAC and your choice of lossy format. In fact dBpoweramp can rip a CD to both FLAC and any lossy format of your choosing in one simple step, and it will use the Accuraterip database to confirm the rip was accurate.
Or you can use EAC, which is free, and then use dbpoweramp or another tool to batch convert at a later point. While my i7 makes the process very quick, even a mid-range Core 2 Duo can transcode a large FLAC collection in a few hours, and certainly overnight.
With 1.5 TB drives at $100, hard drive space simply isn't a meaningful concern.
The market for lossy audio formats on private bittorrent trackers shows the strong preference for MP3. A recent statistical analysis at what.cd showed that MP3 was by far the most popular lossy format, accounting for at least 98% of all downloads.
Ogg Vorbis had very few downloads, and Ogg Vorbis uploads were the most likely to have 0 downloads. It's just not a popular sharing format for the reasons I raise above.
That doesn't mean nobody is using it. FLAC has become much more popular as of late, and lossless formats provides the benefit of being able to transcode to any lossy format retaining tags and album art.
I still think downloading, and certainly, riping to FLAC makes the most sense. You then can purchase any DAP of your choice, and know that you'll be able to convert your music to a supported lossy format. Even a relatively old computer can rip to MP3 relatively quickly. Foobar2000 even has a plugin that will do this for you automatically, for DAPs, including the iPod that don't support your format of choice.
BTW, I'm only referring to encoding for personal use. Obviously, when widespread distribution is a concern, you must consider licensing costs, and size becomes a greater issue.
As a matter of practicality, I don't see why FOSS advocates continually argue for Ogg Vorbis and don't talk much about FLAC. It is probably because MP3, and lossy formats in general are considered to be so popular. But, from my experience at what.cd, a private music tracker with over 120,000 members, FLAC is most certainly popular.
It only has about 1/3rd of the downloads of MP3, but by filesize, it's about equal to MP3. Despite the 300% file size difference, many people strongly prefer FLAC. I listen to classical music, and for many albums, FLAC is so preferred that there are simply no MP3s available, or any other lossy format for that matter.
FLAC is open source and not patent-encumbered. It also has an array of great features - wonderful error detection, frame-accurate seeking, extremely fast integer-math decoding (4-5x faster than MP3 making transcoding very quick).
FLAC is undoubtedly the most popular lossless codec. And from what I can tell, as the cost of hard drive space has dropped, and user upload speeds have increased, FLAC has rapidly surged in popularity. I wouldn't be surprised to see FLAC replace MP3 in 5 years as the format of choice for online file sharers.
There are many good reasons for lossy codecs, but as an archive format, lossless will always reign supreme for its audio quality and flexibility.