It corners well compared to a general perception which assumes it corners very poorly. Both sides go to extreme judgement, and so arguments live on.
In reality, it corners only incrementally worse than your typical track bike - maybe by 10 - 20%, but not twice or three times as bad as the general perception indicates. This only becomes an issue when the rider's level increases. Your observation about track days and racing is very good, and provides an answer to your question.
Riding at the level of beginner and intermediate group - mighty 'Busa does just fine. But, starting with the advanced group, and on to racing - 'Busa's shortcomings in cornering become more of an issue.
Keep in mind that of all riders, very small percentage is doing track days - probably in the ballpark of 5% (I personally did a poll on sportbikes.net a few years ago, and it was something around 2 - 3% - I adjusted it to 5% based on the assumption that more riders do track days now than a few years ago).
And I would say that among those riders who like twisty roads, only a minority are doing track days. It is safe to say the following about the majority of those riders who ride twisty roads but don't do track days - they are not riding at the level of the advanced track group, but rather somewhere at the level of beginner/intermediate track group.
And I can tell you from my own experience riding in the beginner and intermediate group on a 'Busa, I never felt that the bike was a limiting factor - I always felt it was me. I ride very conservatively, i.e. I know I am making a turn, and don't need to pray to get around it.
So, the point is - mighty 'Busa corners pretty good unless you are racing or getting close to that level. And what percentage of riders races or rides in the advanced group? I would conservatively guesstimate 1% or less. So, the infamous statement about the 'Busa is wrong for at least 99% of riders.