And what about the rising number of old companies? Look at different industries such as air travel, raw materials, and manufacturing. What I see is Standard Oil all over again, consolidation, incremental optimizations, with a little anti-competitive behavior thrown in to boot.
That's sometimes the problem with us programmers, especially the more naive amongst us. We often believe that File > New is the answer to the world's problems when incremental optimization often is more pragmatic (and as the market shows us, more effective). It isn't sexy but it "works".
I don't know much about Home Depot but I'm going to guess that they got as big as they did (mostly) by introducing optimizations into the marketplace for home improvement products. They are not a monopoly (such as taxi services) that was created by and protected through legislation and can dissolve rather quickly (like it did in Houston this week) with a change in public support.
The tech "startup" community should stop looking at companies like Wal-Mart as evil and start to respect and marvel at the massive amounts of muda they have been able to eliminate from product supply chains. Just because they don't use Node.js doesn't make them disruptable (yes, I'm aware Wal-Mart actually does use Node).