No, the point is that usually fitting things in RAM lowers the budget. So it's well worth doing proper analysis on whether or not you can (a) fit all your data in RAM and (b) if a cluster of machines does not become it's own reason for existence.
Replacing a large number of nodes with a single machine with a lot of RAM is usually a cost savings measure rather than a larger expense (and it saves power too!), and due to a lack of communications overhead and exploitation of the fact that you now have access to all the data in one go you may very well find that your algorithms run much faster.
A distributed solution should be a means of last resort.
Less than 6 machines with 1T each ;) (Assuming the 6 will operate only on local data and will never need to communicate in which case you may well end up with more than 6).
But seriously: the price of RAM for servers is now ~10$ / G.
No, that's a very expensive server, and Dell will charge you a hefty premium for the memory. There are quite a few options that will cost you less than that (of course the maximum capacity will vary).
It would be nice to see an article comparing all the high RAM machines side by side with specs and prices.
The largest machine I have right now will hold 512G and was a run-of-the-mill machine, it was about $5K, I'd expect the more exotic ones to be substantially more expensive but probably not as expensive as the machines linked here.
I can get Octal rank in bulk for ~$1K so that's $16 or thereabouts / G, still not bad for RAM that is obviously going to be sold in smaller quantities. Note that HP or Dell will probably not be happy if you use 3rd party RAM in their machines (if they didn't pull tricks to make sure only their own stuff works!).
(For contrast, that $1K if you'd spend it on HP branded RAM would not even get you four 16G dual rank units...).
No idea if that will work in that particular server but technically there is no reason why it should not. You can establish a relationship with a distributor to get better prices than those that you can find listed. Those 'call for quotes' things can have two meanings: you're about to be screwed or 'we will give you a better price if you promise to not divulge that we did that'.
If you go by the Dell site linked from the article, a PowerEdge maxed out with 6TB RAM (4 sockets * 24 LRDIMMs * 64 GB) will set you back US$444,000 (or thereabouts). They also list 3.2 TB NVMe PCIe cards for US$11,000 each.
