The issue isn't compassion; the issue is hypocrisy. I don't recall Favre or Downey or even JFK supporting the War on Drugs or arguing in favor of imprisoning illegal drug users. (And I'm not certain that Favre or JFK took illegal drugs. They may have received painkillers prescribed by their doctors.) If Rush illegally purchased drugs, then he deserves the same punishment he has advocated for other people who've done so.
No, actually he should suffer the same consequences that others of his status (but not his caliber) have suffered: rehab. Oh waitaminnit, he did that voluntarily. Downey had to be convicted before he went, and I don't think he was taking whatever he took for "the pain," unless it was the pain of less than stellar appearances on Ally McBeal.
Did Imus ever go to prison? Hmmmm, don't think so.
And the "100 pills a day?" A doctor called in locally and stated that this would be "incompatible with human life." But hey, if Imus wanted to prove him wrong....