450D(?) ISO changes with 1 click, not 3, for full stop?

Was showing a friend some settings etc on his camera the other day, teaching him how to shoot manual mode. It was an xxD model, think it was somewhere around a 450D, maybe 500D model. I've personally only ever used 30D, 40D, and 5DII.

What I noticed was that to change shutter speed and aperture, the wheel was 3 clicks for a full stop. Similar to my 5DII. But to change the ISO, it was only 1 click for a full stop. I was showing him that if he wants aperture at certain value, then if he changes shutter speed up 3 clicks, then he should change ISO up 3 clicks as well to maintain same exposure. But the exposures were all blown out and I realised that we were actually changing the ISO 3 stops, not 3 clicks.

Just curious if there's a custom function somewhere to bring it into line with the other settings to make it easier for him to remember how to control exposure?

The image quality of the in-between iso setttings are sometimes not as good as the full stop iso stops. Yes, it is changed in the custom funtion settings.
...Terry
edit: I just checked and my 450d/xsi only has 1 stop iso settings available, but my 50d has 1/3 or 1 stop iso settings in the custom function settings.

Ok, so he's just going to have to live with it. No worries. Thanks.