Dissing having more levels may be fine from a theoretical perspective, and yes, noise is the main reason to use ETTR. But...
In the real world (rather than the theoretical one) it is frequently the case that one wants to manipulate the image (open up shadows, for example, to reveal nuanced detail). If you've used ETTR and then "normalized" the image you now have many more tonal level in the shadows than you would otherwise have had.
It doesn't take much time in front of the screen to tell that the benefit of doing this is quite real. And, as with most such things, maybe not in the day to day, but most usefully in the extremes.
You have to move away from the number of tonal levels affecting image quality and start considering noise and signal to noise. A high number of levels is advantageous in producing smooth tonal gradations, but the advantage is lost when the image noise exceeds the quantization step as shown earlier in this thread by Guillermo and discussed at length by Emil Martinec in his excellent treatise
Noise, Dynamic Dange, and Bit Depth. The brightest f/stop of a 12 bit raw capture contains nowhere near 2048 levels but it does have a high SNR.
Exposing to the right increases the SNR over the entire exposure range and the improved SNR is often most appreciated in the deep shadows where noise limits the dynamic range of the capture. According to Emil, raw data are never posterized, since noise exceeds the quantization step, but posterization may be brought by processing (for example, application of a median filter).
In most cases, ETTR improves shadow image quality by increasing the SNR and not by increasing the number of encoded levels. Insufficient levels results in posterization. My experience with Nikon DSLRs (D700, D200, and D3) is that shadow image quality is usually affected by noise and not by posterization.
I encourage you to read Emil's essay which discusses your previous ETTR article in this section
and get back to us on Emil has screwed up things. However, I will not hold my breath while awaiting your reply.