There are different ways of defining accessibility. To most people, they probably think it means making the website easier to be understood by those with seeing or hearing dis-advantages. While I do agree that all web design should strive to make all sites in this manner, for the purposes of this article, we are going to be talking about another angle.
There are many schools of thought on what is the ideal number of choices that should be presented to a reader of a site. Too many might confuse your reader, and too little might project the wrong image of not having enough.
I'm sure somewhere there is a magical number that can tell you what the exact number of choices are, but that number should be determined by what the site has to offer.
If you visit ESPN.com, they have a plethora of choices - in fact at the time of this writing (July 21, 2006) there were 302 possible links to click on - and that is not including the roll-overs if your mouse hovered over "NHL" or any of the other major sports.
Since ESPN is more of a portal, it makes sense that they would have that many links - they cater to just about every sporting event known in existance to mankind, so they need to provide the appropriate number of links so that any visitor can find the topic they are looking for.
Now, if you head over to Nike.com, the home page loads up a flash movie, and it has a total of 5 links found on the page. There are 4 regional choices for the user (North America, Europe, Asia Pacific and Latim America). Once you select your region it opens up to a site that you would expect from a shoe retailer - sizes, models, colors, etc.
Since Nike is not trying to be everything to everyone, their site calls for less options - so that the visitor can focus on what they came to the site for.
So how is all of this related to SEO/SEM?
Traffic from Google can bring you tons of visitors, but if they can't find what they are looking for, you've wasted time and energy getting that visitor to your site. So many times a site fails not because they couldn't get the potential buyer to the site, they failed because the site did not make it easy for the visitor to find what you promised them when they clicked on your listing.
'Nuff said.
-To your online success!
Paul Bliss
www.SEOforGoogle.com 
