I agree with what you are saying. I just bought circumaural open back electrostatics and they are great. Every pair that I've ever bought new are
CA/OB*. The HD25's were presented at a very good price and serve well for bed time listening that rarely goes on longer than an hour.
except my Pioneer SE-50's (CA/CB) , the first pair that I ever bought (PX in VN) and audio knowledge was week at 20 y.o.
a pretty good primer:
http://en.wikipedia.org/wiki/Headphones
Circumaural headphones (sometimes called full size headphones) have circular or ellipsoid earpads that encompass the ears. Because these headphones completely surround the ear, circumaural headphones can be designed to fully seal against the head to attenuate external noise. Because of their size, circumaural headphones can be heavy and there are some sets that weigh over 500 grams (1 lb). Ergonomic headband and earpad design is required to reduce discomfort resulting from weight.[12]
Supra-aural headphones have pads that press against the ears, rather than around them. They were commonly bundled with personal stereos during the 1980s. This type of headphone generally tends to be smaller and lighter than circumaural headphones, resulting in less attenuation of outside noise. Supra-aural headphones can also lead to discomfort due to the pressure on the ear as compared to circumaural headphones that sit around the ear. Comfort may vary due to the earcup material.
Open or closed back
Both circumaural and supra-aural headphones can be further differentiated by the type of earcups:
Open-back headphones have the back of the earcups open. This leaks more sound out of the headphone and also lets more ambient sounds into the headphone, but gives a more natural or speaker-like sound and more spacious "soundstage" - the perception of distance from the source. Closed-back (or sealed) styles have the back of the earcups closed. They usually block some of the ambient noise, but have a smaller soundstage, giving the wearer a perception that the sound is coming from within their head. Closed-back headphones tend to be able to produce stronger low frequencies than open-back headphones.