Web browsers become obsolete over time. Web technology improves over time. If your browser isn't as new as the web technology, you'll be missing out on some of what the web offers. If you prefer a formatted list of reasons, here you go:

• Faster browsing - new technology allow web pages to load faster than ever.
• Safer browsing - new versions of browsers contain the latest security patches.
• More interactivity - new browsers support more interactive web pages such as drag-and-drop.
• More accessibility - new features make it easier for everybody to use the web, even if that just means increasing the font sizes to give you eyes a break!
• It's free! How many things let you get the newest model for free?