Are windows update necessary on windows 7?

This is a big pain. Every other day, a small blue book icon is seen on toolbar and it says "windows update". The computer automatically will update and then in the middle of the task it would restart and there would be messages like "configuring 32% complete" "configuring 1 of 3" and so on. What the heck is this stuff about? This is a very big inconvenience and waste of time. Also these updates increase the size of OS and then it occupies more space on hard drive. As a result the hard drive keeps getting bloated and bloated as these frequent updates go on. Hard drive space is not a problem on laptop or desktop as I have 500 GB HDD. But I also have a windows 7 tablet computer which is 8 inches and handheld. It has 16 GB HDD and already 14 GB is full. The updates would totally consume the entire hard drive. So should I disable updates on tablet pc because its such small hard drive? Why couldn't Microsoft design OS which never needs these annoying updates? This stuff is so primitive and stone aged. Microsoft says these updates are for security. But I thought antivirus and firewall are already there for security.