Whether a password system stores your password in plaintext has NO CONNECTION to if it is case sensitive or not. Plenty of badly designed systems require case sensitive passwords but store them in plaintext.
As to whether or not you should be concerned, any system that does not require case sensitive passwords has greatly cut the amount of unique passwords in half or less. It may be convenient to the user, but for example, an 8 character password that's not case sensitive has 208,827,064,576 (208 Billion) possible variations. Case sensitive? 53,459,728,531,456 (53 Trillion) combinations. The amount of time a brute-force cracker needs to run to find your password is so much smaller when Case is not an issue. Add digits (0-9) and that number quadruples to 213 Trillion.
Of course, users tend to ignore good password security features, like using strong mixed character passwords, not reusing passwords, changing them regularly, not using dictionary words, so they may have made a decision not to require too complex passwords.