His example is unclear, but he's complaining about the behavior of conditionally casting the initial data values based on pattern matching.

   <div id="test" data-foo="1.1"> 
   $('#test').data('bar', '1.1');
   typeof $('#test').data('foo'); // number
   typeof $('#test').data('bar'); // string

If the data-foo value is user input, then converting it to a number might not be expected. E.g.

   <div data-emoticon="0.0" />

Yep, latchkey, I think you might want to rethink the article. As others have pointed out, you're seeing JavaScript's behaviour, not jQuery's. And this:

  elem.data('foo', { 'a':1, 'b':2 });
  elem.data('foo'); // Returns the object

Is certainly more desirable than:

  elem.attr('foo', { 'a':1, 'b':2 });
  elem.attr('foo'); // Returns "[object Object]"