@IssaacL. You are right that most people don't know what a disruptive innovation is. That derives from too many believing that it means "innovation" of any kind, or "better" than anything else in the market because they equate the endgame (the disruptor usually ends up with dominant market share and the best product, but only after many product cycles) with what creates disruption, and they aren't the same thing.
However, your brief definition skims over way too much of the theory. Disruptions don't always have to be cheaper or "worse" in the qualitative way that is generally understood. To disrupt, an innovation simply needs to be substantially better on a dimension that the new market cares about, while being referentially worse (compared with incumbents) on a dimension that the existing market and incumbent producers care about strongly (and therefore aren't incented to compete against the disruptor until it's too late).
This is a completely consistent with Christensen, and also with market reality. However, Christensen was wrong about the car because he didn't follow his own logic. Do you see buggy and horse whip manufacturers anymore? Do you see people raising horses for transportation? How about trains as the primary (dominant) form of mechanical overland transport of goods and people? Cars were initially "worse" in that they spewed lots of dirty soot into the air, required fueling stations that didn't exist, could only drive on paved roads (which also didn't exist), and broke down constantly (which meant everyone that drove one had to be a mechanic). But, motorized vehicles were also superior in that they could go faster for very long periods of time without needing rest, they were cheaper per mile to operate than a team of horses, and they were fun to drive, offering a sense of freedom. Cars disrupted lots of things -- you just have to identify the right market and the cause of its disruption.
The fact that the very first cars were really more hobbyist or wealthy-man's toys is irrelevant -- so were PCs until they became economical and found their niche through VisiCalc spreadsheets.
The fact that Christensen wrote the seminal books and made the observations from which the theories were derived doesn't mean either that he is always right, nor that he always applies the theories correctly to predict disruption. He famously declared both the iPod and the iPhone to be not disruptive at their introduction, yet they are archetypal examples of disruption.
In 1949, Thomas Watson Sr, IBM's then president famously declared that he couldn't envision a need for more than 12 computers to satisfy the needs of the entire world. Sometimes we're too close to things to see the forest for the trees.
Also, the Wikipedia article has been overwrought by many techies who think it's about technology, and as such isn't an entirely accurate or good summary of disruptive innovation. In that respect, you are correct -- technology is neither necessary nor sufficient for disruption to occur, but correct market segmentation and positioning strategy, having the minimum viable feature set to satisfy an unmet or underserved need, targeting a market slice that is willing to pay to have its problem solved at a price that you can afford to make it are all critical properties of disruptive innovations, and they are entirely about marketing and business model, not about technology.
Still, we all know that the majority of disruptions are enabled by new technology because it can create opportunities to solve unmet needs at a price point acceptable to an unserved market.
I don't know if that better answers the original question, but it is sometimes, although not frequently the case that disruptive innovations are more expensive than what they replace. The iPhone is a great example of this, as is the original IBM PC which was far more expensive than the PCs that came out of the late 70s, but had the big advantage of IBM's imprimatur endorsing it plus an open architecture, which attracted apps and an ecosystem of vendors springing up to support it.
There is an ebook discussing the widespread misunderstanding of disruptive innovation and why it matters available at http://tiny.cc/disruptve_confusion_ebook