I have heard people say that they won’t bother implementing accessibility on their site because no matter what they do, they can’t make the site work for everyone in every situation. They are right, there is likely to be someone facing barriers on a site, at some point, because their disability has not been catered for. But their conclusion is wrong – the idea is to implement as much accessibility as possible. We can build accessibility into a site incrementally. WCAG 1.0 is presented that way, with three levels of compliance.
The typical example used is that of an individual who is blind, deaf, and paralysed from the neck down. Obviously, the access needs of some people are such that they can’t be met easily (or practically). It is the same with building accessibility. The Americans with Disabilities Act (ADA) says that doors require a 32" clear width to be deemed accessible. Yet, some people’s wheelchairs are so wide that these doors do not meet their needs. It is unfortunate. But we can’t say "because we can’t make it accessible for one person, we’re not going to make it accessible for anyone", and put in a 24" door! Or let’s consider the case of ramps. Again, the ADA states that ramps have to have a gradient of 1:12 (going up one meter for each 12 meters of horizontal travel). This gradient is quite steep for many people, and a ramp of 1:15 (gradient for a bicycle ramp in Australia), or 1:20 (gradient for some ramps in the UK) would be better. We respect the guidelines, and when we can, we go beyond.
So we implement things incrementally. Focusing on Priority 1, then Priority 2, and then Priority 3. And it might be that we can implement all of Priority 1, and only some of 2, and some of 3. But the more we implement, the more accessible the site gets.
Some talk about "greatest bang for the buck". We have to find the place where results and effort meet. How much can we implement without taxing our resources. In general, you can achieve a lot with relatively minimal effort.
And of course you have to look at your target audience. It just might be that your target market has specific accessibility needs that you would not normally implement on a site, yet, because of your market, you’ll do it.
No, we won’t be able to make every site work for everyone in every situation. But we certainly can head to maximum accessibility!