Play for free infinitely

Accidentally played game for free without buying. My nephew wanted to preview Minecraft to see if he would like it, but the in-page client on the website wouldn't load the game on his MacBook. So we downloaded the client to see if it would offer a trial play mode, like on the website. We tried to log in on the client; when it failed, it offered to let us play offline. Seeing he got on, still thinking it was a time limited play mode, I did the same on my laptop so we could play together. It was 3 hours later we realized we were still playing.

Main issues:

1) Website allows client download without purchase.
2) Client allows offline play without successful log-on.

I reproduced this on two Windows 7 PC's, a Windows Vista PC, and my nephews MacBook, which I think is running Lion, or whatever the newest version is.

I don't know if this is still a problem in v1.4.6, as I can't update the client without logging in, and the client available for download on the website is v1.4.5.