Even though it is safe to remove older versions of Java, you may still want to keep some of them in case you have applications which were designed to work specifically with a certain Java build. The catch is that you may not know what Java version is required until you uninstall your old ones and then find that certain online applications no longer function properly.
Java is sometimes odd in that newer is not always better. Some people may say the same about Windows updates. I know from personal experience that updating Java can sometimes cause issues with online applications, and I recently experienced an issue with an online timeclock application at my work after updating Firefox. This is why older versions get left behind on your computer - It's to guarantee compatibility despite the updates.
If you update Java or remove an old version and find yourself wishing that you hadn't, be sure to read my article on how to update or downgrade Java in Windows. Luckily, you can still download old Java versions from Sun Microsystems.
Can you remove old Java updates? Yes you can!
Should you remove old Java updates? Only if you need the extra hard drive space.