yes it seems that variable JPEG compression is getting more and more popular, especially in consumer DSC's. Calvin Hass, the author of JPEGSnoop, has a good writing about this:Variable JPEG Compression
His software also offers a function to scan an executable for DQT tables, so theoretically one could scan a firmware files of cameras for all possible DQT tables. As always, there are some exceptions, e.g. the Sony H series uses integer prescale values to adapt the DQT tables to some shooting conditions (according to Calvin's writeup).
Very interesting topic, but one of the "miracle inside an enigma" type ;-)- Franz