The Denon headphones are 25 ohms, but yes, that is such an example. Orthodynamic is Yamaha's marketing term for planar magnetics. But yes, 100% agree that Z does not correlate to bass quality.
Not really. It's simply a specific of the driver - there are plenty of very high end audiophile headphones that have low Z (DX1000, D7000/D7100, RS1, GSK, PSK, ATH-W series, etc). Years ago there was (there still is, actually) an IEC specification that said amplifiers should target a 120Ohm Zout, as this will drive most all headphones properly (which is true), but that's very hard for portable players to accomplish. So very low Zout is not uncommon. A lot of headphones have accordingly moved towards the more sensitive and low Z side to match up with iPods fairly well - examples include the Beats Pro, T5p, and D7100. There isn't really any advantage for Z differences except when we're talking about portables with limited Vrms outputs (which is due to their batteries). For mains powered devices, it really doesn't matter - your receiver can drive anything from an A.00 to a T1 with relative ease.
Not true. They are usually older in design and higher Z was common - for a few reasons including noise rejection, targetting the 120Ohm spec, and simply part of the design characteristic. Power requirement is dictated by Ohm's Law and sensitivity values. Most studio equipment can provide enough power to destroy any headphones - high voltage or high current, doesn't matter. Again, it has mains power behind it.
Sensitivity and impedance are NOT inter-related in this manner. Low Z does not always correlate to high sensitivity. However impedance specifications can obfuscate sensitivity ratings (as can stating them in dB/V - dB/mW is more appropriate imho). The generalizations about solid state/tube are also inaccurate.
Also inaccurate. And "large" is very relative.
Not a single headphone in current production requires multiple watts of power. By a longshot.
Impedance is complex resistance in an AC system - nominal is the only way to represent it without a 2D graphic.
http://en.wikipedia.org/wiki/Electrical_impedance
http://en.wikipedia.org/wiki/Nominal_impedance
No.
I'd agree with this, but I'd say the "optimal way of driving it" thing is based more on various wives tales and myths than anything founded - tube vs SS doesn't really define that ability, it's just that many cheap OTL amps have poor current delivery and high Zsource and are therefore unstable with those loads (just like most cheap receivers can't handle 4 ohm speakers). With an OTC design, or a quality OTL, such considerations are generally irrelevant.