Because some of your apps don't run the article isn't true?
There are now well over 200,000 Android apps. They are only claiming that 60,000 of them work on tablets. When you consider that number includes apps made specifically for tablets, that's not even 30% of the standard Android apps. (Still wondering where they got the 40% figure... maybe old app count data)
Of course we will all find standard apps that won't run on a tablet. That doesn't make the 60,000 claim untrue.
I'm in the semiconductor side of the biz and often hear scuttlebutt about directions and plans. That info, and $5 can get you a cup 'o joe, but... I heard that Google originally didn't want to have a tablet apps section in the market. They wanted to say everything worked. Let Apple take a black eye for needing two separate sections. Their hoped the only differences between tablet and phone apps would be scaling and that would take care of itself over time. They were wrong, of course, with all the force closings and unintended degradation of system performance (lagging). When it obviously didn't work out the way they hoped, they had to change course. Hence, the delay we all saw with regards to the introduction of a "Featured Tablet Apps" section.
IMHO, Google still hasn't let go of their original premise. That's why we only see a "Featured" area in Market and not a dedicated expanding repository of all tablet apps.