Maybe this will explain...
Yes, in a somewhat perverse turn of events having finally got the flight sim cockpit set back up, the first thing I've done is use it to play a truck driving game. Now I'm not a particularly big fan of trucks or trucking, but to be honest the reason I bought ETS2 and the reason I mention it here is that for me at least, it hits a lot of the same buttons as flight simming. They're both journey-based simulations, where the objective is simply to get from A to B in a timely and safe manner. They both involve controlling large vehicles that many of us will never get the opportunity to control in real life. Both have lots of nice simulated scenery to enjoy.
ETS does approach things a little differently, with more focus on giving an enjoyable game rather than a strict simulation. The simulated world extends across most of western Europe (with an upcoming DLC extending that further into eastern Europe), but at a time and ground scale of about 1:12. That means that for every five seconds of real time, a minute ticks by in the game world. But since the scenery is scaled down to match, you're still driving in "real time". It's a good compromise - I really wouldn't want to be sat simulating a five-hour drive in real time, and the journey and game-world times seem to match reality fairly well. The road networks are based on reality, though the city streets are greatly simplified to give a good impression of the sort of industrial/commercial zones that trucks might deliver to.
The motorway network (I've only really driven in the UK, both IRL and in the game, so I can't really compare the continental roads) is a decent approximation with a few irritating diversions from reality. In reality, many if not most motorway junctions in the UK are roundabouts. If you miss a turn-off, it's usually simply a matter of waiting for the next junction and doubling back on yourself. That's not possible in ETS, which means a missed turn-off can result in a hundred-mile detour (I missed an exit on a trip from Cambridge to Manchester and wound up crossing the Humber bridge on the resulting detour). Some of the motorway routes are a little wacky as well - IRL the journey from Manchester to Liverpool is a simple matter of heading straight up the M62, whereas in ETS2 the sat-nav gets you to turn off and take the southbound M6 and then the M56 (which in reality takes you to Runcorn and the Wirral). Finally motorway service stations are directly next to the motorway carriageway, rather than being set back or concealed by scenery as they almost always are. This last is probably an artifact of the scaling down factor, but it does break immersion a bit if you're used to driving on motorways.
Another area where the game falls down as a simulation is the flight model... sorry I mean driving model. While it does give a decent impression of driving a heavy goods vehicle, it doesn't do anything to differentiate between the different models of truck available, so a Scania will feel and handle exactly like a Volvo, which will handle just like a Renault etc. Customisations and different specs do change the handling, so a 700hp engine will have more oomph than a 540hp one, and a six wheeled chassis will have more stability than a four wheeled one.
But where ETS2 scores highly is the career/business side of the simulation. You create a character representing your driver and build up his or her skills and reputation by taking on contract jobs driving for other companies. Once you have enough money in the bank you can buy your own truck and drive as an independent operator, then move on to buying more trucks and hiring drivers to work for you.
I never thought that I'd enjoy a truck driving simulator. But it gives a lot of the same enjoyment that I get from sim-flying, with the added bonus of a compelling career game. I can see some interesting possibilities for synergy between FSX and ETS - How about shipping goods by road to a city with an airport, flying it out to the continent, then driving the last leg to a final destination?
Back into the air, and on to the issue of FSX's no-longer-functioning real world weather. After reading an awful lot of reviews and opinions, I've bitten the bullet and picked up ActiveSky 2012 as a replacement weather engine. From what I've read, while it does offer a lot of features and fancy texture controls, it is possible to use AS2012 transparently, having it sit in the background and inject real-world weather into FSX seamlessly without further intervention. Since that's really what I want... the ability to jump in the sim and fly a flight today, real time with the weather that's outside my window right now, there doesn't seem to be an awful lot to choose between AS2012 and REX Essentials with Overdrive. I've just finished the download and am about to install AS2012. Fingers crossed.