Yes, but they don't support Tiger and those old versions anymore either but they don't expire.
Apples and oranges (pun intended), supporting an old release OS and a beta of an OS are completely different.
If you are someone you wants a new OS and
you choose to install a
beta of a new OS you should understand along with it possibly being buggy, laggy etc. it doesn't have full support from Apple (and has none after said OS releases). Now the release version is 100% free, now why
wouldn't Apple make the beta expire?
By making it expire they avoid having to turndown people from support, people having bugs, third-party incompatibilities all of which would taint their image.
When would someone want a new OS, get a beta OS which doesn't have full support, not update to the free release version and then have a problem with the beta having a expiration date? That's not going to happen much (if at all).
By having it expire you inconvenience/annoy just about nobody and you save yourself and other people from headaches.