Well, I think the takeaway is that as you increase the number of drives, you have to carefully consider the attachment hardware you plan to use.
For example, I know that people who are comfortable with the idea of building their own system "affordably" often trend towards the Norco chassis, because they are inexpensive. However, without an SAS expander, the number of "adds" you have to do, to add a power supply, fix cooling deficiencies, figure out how to arrange SATA attachment for large numbers of drives, I'm not sure the added frustration is worth any possible savings. You're adding extra dollars, and maybe extra controllers and extra watts.
On the flip side, Supermicro's backplane-with-SAS-expander option is somewhat limiting in the bandwidth available to the backplane (x8 wide porting didn't seem to work but I didn't investigate too deeply). For non-extreme-performance NAS uses, it ought to be perfectly acceptable. If all you have is an X9SCA with an E3-1220L and two gigabit Ethernets, you are definitely in the "non-extreme-performance" realm. As a practical matter, today's standard SATA drives like the ST4000DM000 probably peak out around 150MBytes/sec, which is about 1.2Gbps. Of course there's overhead not factored in there. So let's say 1.5Gbps per disk. For a 12 drive chassis, that means 18Gbps. For 24, 36Gbps. Well, a single 4 lane SAS SFF8087 gets you 24Gbps.
There's nothing magic about Supermicro's backplane-with-SAS-expander by the way. Except the cost-to-solution winds up somewhat better IMO. Buying preintegrated stuff from an OEM is often cheaper than beating your way through the retail product maze.