CS5.5 was a paid upgrade from CS5. As far as I know it is no longer available at all on the primary market, and you should be very careful about any purchase on the private sale market -- you can easily wind up with software that cannot be registered. Your upgrade options now are to buy a perpetual license for CS6 (I don't know if there is still a discount for CS5 users), or buy a subscription to Creative Cloud, and with that you get access to CS6, CC and CC 2014 versions, as well as new releases as they come out, for as long as you pay the subscription fees.
As far as making it hard, you had plenty of time to upgrade to both CS5.5 and CS6, and there were no secrets about the new subscription model or the discontinuation of perpetual licensing and upgrades for anything earlier than CS6.