Updating the iPhone 3GS

Question

Every single time that I had to update my iphone I have gotten an error. Each and every single time I had to wipe it and reinstall everything. 3.1.2 is no exception. I'm trying to find out why, but I have no idea what could be the issue.
Before even downloading the update, I make sure to close my firewall. I check if iTunes is at the latest version. Nothing else is running on my pc that could interfere with the process. Ports are open, and so forth.
Is this intended by Apple? That at each upgrade, a forced Restore must be made to successfully upgrade it? I'm a little disappointed with this process and I lose quite a bit of time each time to set it back up.
Is it something that I'm overlooking that would cause an error to happen during the update process?
And, finally, is there any way to check (manually) if the download package that iTunes automatically grabs is corrupted before installing it?

Answer 1

@maxeym
If it's not being recognized by the computer, first thing to try would be to uninstall/reinstall iTunes to make sure software is working properly. Then attempt to use Recovery mode to perform a factory default. If the phone still doesn't get detected on your machine, try a different computer if you can. If that still doesn't work, you'll have to try an Apple genius because it's likely a hardware issue.
If your phone does end up getting detected, but recovery mode doesn't work either, try a restore from DFU mode. DFU doesn't load the OS, so it's less prone to problems.
http://techierambles.blogspot.com/2009/09/restore-iphone-with-error-13-or-1611-i n.html
To enter DFU mode:
1. Connect your iPhone to your computer
2 . Turn iPhone off. You may have to hold the power and home buttons down together to force the phone off
3. Once the phone is off, hold the power and home buttons together for 10 seconds exactly
4. After 10 seconds, release the power button but keep holding home until the computer recognizes that a USB device was plugged in
5. iTunes should detect your iPhone correctly, and also allow you to restore to the factory default settings