Haha, I've fixed computers a couple of times with that many infections as well as some that have had many variants of Virtumonde clogged up in Windows. Believe me, it's really time consuming when Avast and Spybot cannot remove the garbage. Also, I typically tell people when they get pre-builts to just erase the hard drive and start new, then begin with new software. Not only is the system going to be faster, there's less of the OEM junk on there which HP and the other carriers seem to love to do. Like HP, they put a security/PC Tune Up Center on their computers that only sees the anti-virus that they install, as well as with some Google Stuff and HP suppport, with Norton. Dell, they've started to ease up. Only the Dell Support Center and some Google software, and anything you ask for. Emachines, they've been pretty light but I've noticed they'll cram two anti-virus programs into one system. I typically uninstall both or reformat the box and then install Avast (used to install AVG, but that's gotten bloated really quickly). Emachines does also use some PC updating program which is like Automatic Updates, but it is a bit more annoying when it pops up every 2-4 weeks saying there's a patch, rather than downloading it and installing it. It's called BixFix.
Compaq, Gateway, and the others, can't really say. I do know Gateway installs BigFix and some Google software, but that's just about it. I know of some people who have paid for McAfee and Norton, and I've always told them that if they wanted to save some money, that I do use Avast and that it's free just as long as you renew the subscription every year. They were happy to hear that, especially after I found viruses on their computer even after McAfee/Norton, fully updated was installed and scans had been run.
I know this because I'm always cleaning people's computers out for them. They're suprised when they see that all of the stuff that the computer maker installed was actually just junk or was slowing down their computer. After a good uninstallation of many programs and some nice clean out of System Restore and then a defrag, they're always surprised to see 15% of their disk space freed up (if their drive was really that full).