Yes, you do.
http://articles.chicagotribune.com/...04_1_new-illinois-law-construction-zones-lane
First of all, I may very well be wrong about the 1/4 mile rule. It's been about 5 years since i looked into it, and was provided by a lawyer language from the state that said a 'safe pass' is one that can be made within a 1/4 mile. I vividly recall seeing the statute at that time; but for the life of me I can't find it now or back it up. The idea of 'you can only be in the passing lane for a 1/4 mile" comes from the law that says you can't be inthe left lane except to make a pass, and you can't make a pass unless it's safe. And it's not safe unless you can make it within 1/4 mile.
So I'll own that one because I can't back it up. Got me there.
However, in regards to what you quoted, the law, including the links I provided, very clearly say.
1) You can't be in the left lane unless you're passing traffic.
2) You have to move over if someone wants to pass you.
This means if you're doing 70mph and passing some cars, and I'm doing 80mph, you need to move over for me and let me pass you. Nothing more, nothing less. Get out of the left lane if someone wants to pass you. Let them pass, then get back into the left lane and continue passing the other cars.
http://www.ilga.gov/legislation/ilcs/fulltext.asp?DocName=062500050K11-701
(625 ILCS 5/11-701) (from Ch. 95 1/2, par. 11-701)
The statue literally says you can be in the left lane only to pass vehicles and but NOT if there's a vehicle directly behind you when you're in the left lane. It clearly says if you're in the left lane and someone is behind you, YOU ARE NOT ALLOWED TO BE THERE ANY LONGER.