Induction loop systems are much more common in the EU and down under than in the US. I believe that the UK virtually requires them in the DDA, their version of the
ADA, while the US allows for wired, IL, IR or RF systems. I've seen references that 90-95% of hearing aids in the UK have integrated T-Coils while in the US it was I believe the number is somewhere around 50%, but apparently that number is rising as it was around 30% 10 years ago. People here are seemingly more concerned with the aesthetics of hearing aids and thus more likely to want them as small as possible, which means not including T-Coils. Add that to the fact that many people who might want hearing assistance in
theatre, church or other similar situations do not wear hearing aids full time and I've seen estimates for the US as low as 12% to 15% of the people who could benefit from
ALS being expected to have T-Coil compatible hearing aids.
Another factor is that while just about anybody can install an RF
system, IR and IL take a little more consideration. An induction loop
system must be properly designed to both work effectively and not create problems for other devices, especially in retrofit situations. IR and RF systems are typically more amenable to multi-channel simultaneous
ALS and interpretation use, a consideration in some applications.
Induction loop systems are pretty much inherently limited in
frequency response. The T-Coils virtually have to filter out 60Hz (US) to avoid getting hum from
power systems so that limits the low
frequency response while losses inherent in the loop and transmission tend to limit high
frequency response. The
IEC spec for
frequency response of IL systems is 100Hz-5,000Hz, +/-3dB, although some systems do exceed this.
Added: Trying to avoid a political discussion as this is not a political statement but when the government or a national health plan provides hearing aids for anyone that qualifies, then more people are likely to get hearing aids. Those groups then also control aspects such as requiring that t-coils be incorporated in all hearing aids they provide. So there is probably a pretty direct relationship between who would have to pay for the hearing aids and what choices the users have in the specific models to the percentage of the hearing impaired population that can be expected to have induction loop compatible hearing aids. This is probably one reason why the numbers in the US have been so low compared to many other countries.