Providing support for outdated software is both unexciting and expensive. If people are still using the version which was sold ten years ago, it means that they will find bugs which do not exist in next versions, their software may not work as expected on a new hardware or operating system, etc. The support people must also be trained to use this old version.
This is unavoidable in several cases:
When every next version of the software is paid, you can't force everyone to spend their money every two years to buy the next version. Example: Microsoft has still to support Windows XP, since it is understandable that people don't want to pay hundreds of dollars for Windows Vista, then Seven, then Windows 8.
When the update is complicated. Example: when you know that installing SP2 of Microsoft SQL Server 2008 may render your server completely unusable, you may want to postpone installing updates and stay with and outdated version which has one strong point: it works.
When legacy systems or security considerations are involved. Example: auto-updating a space shuttle software every week may have some disadvantages. In the same way, you can't update hardware if the legacy software requires the old hardware to run.
Now, let's say that the update process is as well done as in Google Chrome. The user doesn't have to bother with the updates; there are no security or legacy reasons to not to update, and the updates are free.
In this case, is it a bad practice, for a company, to stop providing any support for the versions outdated for a few months, and ask their customers to update their software first, then contacting the support if the problem persists?