Why WCAG made 3 level "A", "AA" and "AAA"?

Question

What is the purpose of making 3 priority level by WCAG?

is it like?

• If client not paying extra or if we don't have much time then go for A
• If client paying then or if we have time to make site compatible go for at least AA
• If client paying and needed according to govt. rules then go for AAA

If we are making site then which level we should we try to achieve, or we should do only on client request?

Although i found these definitions on this site but these are confusing for me

• Priority 1: For all users to access the Web content and for Web developers to attain Conformance level “A”, these requirements must be satisfied.

• Priority 2: These requirements should be satisfied by the Web developers so that no group finds it difficult to access the Web content and so as to attain Conformance level “AA”.

• Priority 3: These requirements may be satisfied by the Web developers to facilitate access to Web content for some groups and attain Conformance level “AAA”.

Answer 1

WCAG 2.0 is divided into three conformance levels (A-AA-AAA) because the success criteria are organised based on the impact they have on design or visual presentation of the pages. The higher the level, the more restraining it becomes on design.

For example, let's take guideline 1.4 (Distinguishable), which is about making it easier for users to see and hear content including separating foreground from background.

• Success Criterion 1.4.1 is about the Use of Color. The rule goes like this: Color is not used as the only visual means of conveying information, indicating an action, prompting a response, or distinguishing a visual element. (Level A)
• Success Criterion 1.4.3 is about Contrast (Minimum). The rule goes like this: The visual presentation of text and images of text has a contrast ratio of at least 4.5:1, except for the following: (Level AA)
• And finally, success criterion 1.4.6 is about Contrast (Enhanced). And the rule goes like this: The visual presentation of text and images of text has a contrast ratio of at least 7:1, except for the following: (Level AAA)

As you can see, the more higher we get, the more demanding it becomes and the more pressure it put on how things can be presented in the web page.

As a rule of thumb, success criteria from level A should be invisible or barely noticeable to the interface. On the other hand, level AAA will have such a high impact on design, that even the W3C claims that most organizations will not be able to achieve that level (as the compromises on design will be too important):

Source: http://www.w3.org/TR/WCAG20/#conformance-reqs (WCAG 2.0) - from the W3C

"Note 2: It is not recommended that Level AAA conformance be required as a general policy for entire sites because it is not possible to satisfy all Level AAA Success Criteria for some content."

Working towards compliance to one conformance level or another in any given project shouldn't have anything to do with what the client pays or doesn't pay. It should always be about making everything you can (within the boundaries of resources and budget of course) to ensure that all users, regardless of disabilities or limitations, can enjoy the content that is provided to the public. And this is especially true when it comes to government content.