Love this! Just discovered that I'm paying a monthly membership to my fiance's old gym when she hasn't been there FOR OVER A YEAR...because she moved and (thought she had) cancelled it.
The gym is an interesting special case because there really is value in the commitment device of "I paid for this gym membership so it will feel really wasteful if I don't go all month". Our second biggest competitor -- http://gympact.com -- turns that aspect of gym pricing up to eleven, charging you more for not showing up (and giving you a kickback if you do).
As far as auto-canceling subscriptions, the gym could also make an argument that they have to provision a lot of physical space and equipment based on how many people have paid to use the space. They don't recover that cost when you don't happen to show up.
None of this applies to most SaaS companies though!