You write "[...] the use of these techniques is
not always indicated on album packaging." At least in Germany this
now isn't true anymore.
I just bought the Strokes album from an on-line store, and I was upset
to find out on opening the packaging that it was 'corrupt'. However,
the CD played perfectly on my Linux box without DRM of any kind, and
in my wife's car CD player too.
So I'm inclined to think that a lot of these warnings are bluffs - the
label wants you to think the disc is non-standard, but the shops
don't want all the returns and the bills for broken hardware.
However, the consumer rights programme on BBC Radio 4 had an item
recently about CDs that won't play in cars, so the info about DRM is
slowly getting through to the general public.
Cheers
Daniel