You are correct from a practical viewpoint. However, technically speaking, there ARE Bluray players which generate CC (line 21) and Bluray discs which contain CC (line 21). I use them in my lab and for production testing quite often.
The problems are (a) like DVD players, not all Bluray players generate CC. I bought 4 different Bluray players models and found two did and two didn't. I just returned the two that didn't, and bought two more of the ones that did, but that isn't practical for a typical consumer. (b) very few Bluray moves have CC - when I last shopped about 2 years ago, I guess it was only 10% of the available titles.
Finally, even if you have a Bluray player that generates line 21 CC, and you have a Bluray movie containing CC, chances are you want to enjoy it in high definition (component or HDMI connections). The only way to see the line 21 captions would be to watch it using the composite video.
However - shameless plug - as I've mentioned on the forums here before, I have a box that passes HDMI video, and also decodes a corresponding analog video signal containing line 21 data. In this way, I can overlay closed captioning data onto video from a Bluray player (or most other HD video sources). The hardware is in production now, but the software only supports POP-ON mode captioning to-date. I'm working with a beta tester, and hope to have a full-feature unit ready in the next month or so, supporting ROLLUP and PAINTON styles as well (not so sure about TEXT, though that's way less common).