I find it very hard to believe that the ACARS system on Malaysia aircraft do not have SAT connectivity.
What is most likely is that MAS does not subscribe (pay) for airframe status monitoring. That requires a lot of bandwidth that they've determined are not worth the extra cost.
OOOI/weather/free text are probably all available to the pilots when the ACARS is using the VHF *and* SAT medium. Additionally, the RR health monitoring is probably paid for by RR and/or MAS as part of the purchase/warranty programme and does transmit via satellite, but only when programmed or demanded.
Snapshots of engine parameters are taken and sent at pre-programmed intervals or whenever something is out of tolerance. What that programming is is known to the engineers.
What the WSJ got wrong was that the Inmarsat network detected "pinging" from the Satcom system itself, not the RR trend monitoring data.