I think that the point is that if you can survive with a MBA with 4GB, then you can survive with a MBP with 4GB and just save the money. The same for the other specs that he was maxing out. He then went on to conclude that the lower specs meant that he might have to replace his laptop sooner, but the lower price meant that wasn't much of an issue. This side-steps the fact that if you lower the specs on the MBP you could say the same thing (lower specs == replace sooner, but lower cost offsets this).
No argument there. However as you start cutting things from the 15", driving the price down, it gets less and less compelling when compared to the 13" Air. The upgraded specs are the only reason to prefer the 15" over the Air at the same price, the Air is 1/2 the size & weight. Of course this is only my opinion, and it's merely a coincidence that I share it with this particular author. I'm not sold on the Air yet though, I think it needs a couple of iterations before it'll be a great Pro replacement and not just a passable one.
If you take the base 15" and add a 128GB SSD to make it as cheap as possible it's $1999. Unless you really care about the CPU, graphics card, optical drive, or FireWire (which I don't, but others do) you're paying $200 more for a larger, heavier machine. With less storage. If you add the 256GB SSD it's $2399, which makes it even less compelling. I'd rather put that $600 towards a 27" display and still have a 256GB SSD.
The only reasons for me to prefer the 15" are greater resolution or memory capacity, without those I only benefit for the faster CPU. Again this is very much my opinion and I don't expect everyone to agree. I'm not baffled that we disagree, people value different things based on their usage patterns.
