Firstly, I'll assume you're talking about expensive Swiss 7750 replicas, otherwise the difference is obvious: The Asian 7750 isn't an ETA.
Secondly, IWC replace rather a lot of parts in their 7750. Even the Swiss 7750 movement isn't the same as an IWC 7750.
The proper Swiss SFSO had an ETA 2824, which was the exact same part as was in the genuine Breitling.
As for the FM Conquistador with the 2892, you'd have a hard time finding a new one these days that's not got an ST18 in it instead of the gen Swiss part.