GatesAir, possibly now separated from Harris, still lists AM transmitters to 2Mw on their website. http://www.gatesair.com/products/transmit-radio/am-transmitters
I notice that those transmitters are solid state, also. I've seen guys talk about solid state MW transmitters on one of the pro-oriented radio discussion forums, so I know they are in use at a lot of MW stations, at least here in the US.
That was what I was trying to infer. A lot of the big MW stations in the US have the newer equipment. However, the RFI setup at Allouis was likely ancient, since the Allouis outlet had been on the air so long. I know that when the US govt shut down the big SW facility in Delano, California, the army asked a few amateur radio clubs focused on boatanchors if they wanted the setup. The hams were baffled until they saw that the whole facility had equipment made by Collins in the early 1950s! My understanding is that the main transmitter will be preserved.
Since most radio stations in the world are owned and operated by govt's, it's likely that a lot of these old stn setups are ancient, since nobody wants to spend money to replace them. Heck, the IRS still uses mainframe computers made by Sperry Univac! The IRS has to fly magnetic tape all over the country since the computers can't communicate with each other.
Now, imagine maintenance and upgrade of AM stn's in the hands of some obscure agency, one that doesn't want to spend money to upgrade. So, you have a lot of 60-70 year old transmitters out there, and the parts finally become almost all unobtainium, so the bosses say "eh, nobody listens to radio anymore anyway, so let's just scrap this old junk and buy some servers".
I think that was why the Russians finally scrapped their old SW transmitters-they were likely all old Soviet stuff, and the parts were so weird that it simply wasn't worth it. It IS possible to keep the old stuff running-the Cubans do-but the Cubans have to make do with jerry-rigged fixes.