My assumption there is that with PHL as bad as it can be, you'd want to connect as little as possible to mitigate risks of possible misconnects. For example, if you're flying PHL-SLC-LAX, and things in PHL are bad, you could easily misconnect in SLC if the weather there is good. I just don't think I could bring myself to risk that consistently. Plus the PHL-ATL flight, which includes two of the most delayed airports in the US, strikes me as a disaster over and over again. That's why I was thinking what I was thinking. But of course, it's your choice.