That's not what I said. The point I was making is that replicating their hardware functionality is a small part of the puzzle. Their customers are buying solutions and trust, not just hardware. So even
if you replicate everything, they still have a business.
That said, there is plenty of high end networking gear that is hard to replace without getting into similar price territory. If you're going to be handling throughput in the tens of Gbps per line card, with high enough availability to require everything (CPU, line cards, RAM) to be hot-swappable, you may be able to do that with PC's, but you're going to be looking at high end, high margin specialist servers of the type you won't be buying in a local store.
And even assuming you can save on the server, you'll still be paying for line cards and network cards that are produced in small quantities and that are high margin as well.