If you pay for an ongoing maintenance plan for your website, it will already include upgrades for various components of your website;
Security updates are necessary to protect your website and server from hackers who could potentially cause trouble for you online. Hackers tend to target popular online softwares to find loopholes and work them to their advantage.
Software patches and upgrades are heavily linked to the security factors mentioned above. Script and software developers constantly work on their products to eliminate security holes, improve functionality and add useful new features that make your life as a website owner easier.
New browser support can make or break your website. Considering that the internet and its technologies are some of the fastest changing, growing and developing avenues today, common sense tells us that in years to come, technology will outgrow your current website and leave it behind.
We cannot predict the future, so you need to stay on top of these technological developments and tweak your site accordingly.
This why a maintenance plan is so important!