I've done almost the exact same, written by Starr also.
Squat and DL are done on heavy day as a shock tool for the CNS. It's the same idea as going for a 1 rep max on heavy day for a power lifter. Maximum stimulus to your nervous system leads to increased strength. It may be difficult at first, but until your numbers become large it's not too much a burden. By then you'll need a more specialized program.
2x20 on the DB because you've already done a lot of lifting including flat bench. It gives you a little break on the weight. High reps at this stage in your workout will help with muscle growth and as an active recovery from your heavy sets. You go heavier on the inclines on Friday.
I agree with jennsfitness about which program is 'better'. Madcow's program is a refinement that most likely works better for him and lot's of others. Some will like Starr's version.