Where does "MidFi" differ from "HiFi" or "LOFI"?

"The ear hears from a range of 20-20,000HZ, but mid-range is certainly not at the 10,000HZ level.". 

You need to think in terms of octaves, not the full frequency range. 20Hz to 40Hz is an octave, 40Hz to 80Hz is an octave, 80Hz to 160Hz is an octave. 10KHz to 20KHz is one octave. 

Regarding the Lo-Fi, Mid-Fi and Hi-Fi terms, @jasonbourne52 got it right. Those were terms not invented by electrical and audio engineers, but by sales people to make sure they could upsale customers and make them feel bad if they bought the cheaper alternative. 

They are arbitrary and not related to price much at all. Consider this: Someone listening to a $300 CD boom box might think it is Hi-Fi compared to a "Lo-Fi"  $10K turntable playing a vinyl record with snaps, crackles, and pops. 

@cd318 indeed. This Fletcher-Munson curve has been discussed on here several times. Hence the need (if we are honest) for either an EQ or what used to be termed a "Loudness Button" that would compensate for how the human ear perceives the frequencies below and above that critical 3KHz-4KHz range. 

We all know there are budget components, midrange components, high end components, and cost is nearly no object components and manufacturers try to hit those ranges depending on what market they think they are serving. 

But there is much overlap between many of these devices, and of course a diminishing return as you go up the food chain from midrange to high end. 

If you can get good sound quality with a system costing $15K and you have to spend $30K or more to hear a slight difference in sound, it is up to the individual how much it is worth to them to get that last 5% and whether or not it will ulitmately make them enjoy listening to music more.  That's just it. As noted by others, there are two extremes of audiophiles: Ones who appreciate listening to the music and what the artist is conveying sonically that causes an emotional response, and the others who are listening to their equipment and how it is performing, with most falling somewhere between those extremes.  

It's like DACs. It seems we have those who are just fine and happy with good quality chip-based sigma-delta DACs and those who think anyone calling themselves an audiophile HAS to have an old school architecture R2R DAC. Well, maybe.