Google doesn't really care about the extension, but people do.
When the internet was first getting big, companies sunk tons of advertising dollars into promoting their .com name.
So, everyone has come to expect that legit businesses have a .com
Also, the best domain names for SEO do NOT involve your business name. It's something like clevelandpetstore.com - that is, if you're a pet store in cleveland!
Other good domain extensions are .info .tv(if you're involved in television) or a country-specific extension (like .co.uk for united kindom)