I would venture to suggest that this is still the case, for the same reason. But when you're throwing thermonuclear warheads around, the difference in accuracy with modern weapons is insignificant.
Sure, but it needs to be a tractor-trailer that has all the same external signatures as a live TEL to anything you think the bad guys might get within detection distance. That doesn't just mean the same outer mould line, but:
- Mass and mass distribution. When it goes over a bridge, the bridge needs to deflect identically.
- Thermal signature. A live weapon will, at a minimum, emit some level of decay heat. Are the hot spots in the same places and equally hot?
- Radiation signature. A live weapon will emit some level of radiation. Your decoy needs to be able to mimic that. You can shield it to some extent, but then you're increasing your mass and thermal signatures.
- Chemical signature. If anything in your weapon offgasses, then that's detectable.
- Technical signature: If you've got 1 live launcher and 4 decoys, and only one launcher is fitted with a missile turboencabulator, then intelligence sources can just pull the maintenance records for the turboencabulators. If the decoys have signature emulators, then the ones that don't are clearly live.
- Operational signature: obvious, but not trivial. Your decoys need to be moved like they're live. Full security detail. Full security clearance for everyone who touches them. That's a huge cost.
And that's just the ones I've though of while on a tea break.
Sure, some of these may not be easily observed by satellite. But if you're planning to disperse by road, any competent bad guy is going to have some special operations or intelligence types a mile or two from key choke points with a good telescope and sensing devices.
The technical and operational stuff basically implies that your decoy and live TELs are absolutely identical. Most just have a missile simulator in them, and the rest have a live missile. As few people as possible - and ideally nobody in the missile convoy - knows which are live.
The question then becomes, how much more expensive is it to have more live missiles? If the missile is a low proportion of the overall system cost - either because the missile is cheap or you need a lot of decoys - then it may turn out that decoys don't save money.