Software upgrade always involves a learning curve and many a times we don't upgrade to latest version of operating system or software package just because of this learning curve.
There are users who are still using PowerPoint 2003 or XP and have no plans to upgrade to PowerPoint 2010. Here are few links to tutorials which will help you learn PowerPoint 2010 and make your decision to upgrade.
Microsoft Tutorial: Make the switch to PowerPoint 2010
Titan Tech PowerPoint 2010 Training videos
About.com: Beginner's Guide to PowerPoint 2010
PowerPoint 2010 for Dummies By Doug Lowe