When DVD burners were starting to take over, it seems like Sony, Lite-On, Memorex, and other companies put out a swath of 52x CD-only burners. Here's one: http://www.newegg.com/product/product.aspx?item=N82E16827106084
Now that DVD burners are out, it seems like they will only write CDs at a maximum of 40x or 48x. It's like manufacturers only had the 52x for the marketing hype, and 52x was not worth the hit in quality for a few seconds faster of a burn.
I think the same thing is happening with Blu-ray burners. Manufacturers have decided that 16x is the fpoint of diminishing returns, and have carried 16x DVD writing capabilities over to the Blu-ray burners, instead of carrying over the 24x capabilities. Also, I'm sure the last thing they'd want is someone returning one of their expensive Blu-ray burners because someone got a coaster DVD at 24x. Better to play it safer and only do 16x.