This is not a hardware issue, its more like an unoptimised ROM issue. I suppose it will be fixed with an update in the future.
Leaving WiFi on does not matter because your device automatically goes into standby mode after a pre-defined time (3 minutes by default). In that case, even if you leave 10 apps running in the background, it won't make a difference for the aforementioned reason.
With the HTC Universal, what happened was that people would leave apps running in the background and once they are done using the device, they would just close the device thinking that it would shut off, but it wouldn't because the standy-mode was disabled by most people to get a snappier device. In such a situation, battery would drain rapidly overnight as the device hasn't gone into standby mode.
This situation will occur on the JAMin too IF there is no default standy-by mode set.