That's exactly my point!
My brother-in-law, who's here on B2 visa, won DV2007. His visa expires on October 4th, and I don't think he has a chance extending his visa. So, he is going back to do CP, because he can't risk getting his visa for DV by overstaying the B2 visa. I mean, the 180 days we talked about here would have been more than enough for him to apply for AOS, but IT IS RISKY!
Anahit, for 180 days a person who overstays will be OUT OF STATUS (aka INeligible for AOS), but illegal presence of less than 180 days will not trigger a ban on entering the US for 3 years.
If your brother overstays his I-94 by 1 day, he will be ineligible for AOS, but still eligible for CP (if less than 180 days). But I wouldn't risk that either.