Is there a technical challenge to making the the thrust reversers as reliable as other aviation systems? Are the A380's electronic thrust reversers more reliable than the traditional mechanical or hydraulic reversers?
It's not so much that thrust reversers (TRs) are more unreliable than other components of the plane. However, they have a very important impact on the airplane's performance. Hydraulics, flaps, and even engines fail regularly. But engines and hydraulics can be backed up by redundant systems, and an airplane can still land without flaps. But engineers learned from Lauda Air Flight 004 that an airplane may not be controllable if the TRs deploy in flight.
So in the interest of safety, the TRs have additional precautions. The reasons for not aborting a landing after they are deployed are discussed in your first linked question. Reliability is also not the only reason for having no TRs on the A380 outboard engines, as discussed in the second linked question.
So to answer your question, there is indeed a technical challenge in making the TRs reliable: they absolutely must not deploy in flight. This means many safeguards are put in place, and they are designed to fail by not deploying if there is any doubt about whether it is safe. A TR that won't deploy is more desirable than a TR that deploys when you don't want it to.
I would disagree with the assertion or assumption in the question that TR's as "so faulty" and significantly less reliable than other systems. Based on my experience, the reliability of TR's is probably between 99% and 99.9% -- in other words the times when a TR fails to work is between 1 in 100 and 1 in 1000 flights. That, to me, doesn't look like a particularly bad record.
Modern aircraft in general are extremely reliable, so when you compare a component with a 99.x% record against a component with a 99.999% record (say, a windshield -- how often do you see those fail?), the former doesn't look good in the comparison. But when you consider that there are thousands of commercial flights daily in the US, and it's uncommon for anything significant to make the news, the reliability rate for the system as a whole is extremely good.
Some of this is fault tolerance; on most runways, unexpected loss of a TR doesn't affect things very much. The vast majority of the time, braking performance is entirely adequate to stop the aircraft well before the end of the runway even with no reverse thrust (not merely one of two or one of four failed).
But in over a decade of flying modern jet aircraft, the number of times I've seen a TR fail to deploy I could probably count on the fingers of one hand, so all in all I'd suggest that they tend to be quite reliable.