Edit: Oh, I see you removed your post ;) I'll leave my reply on here anyway for people interested in what the Ext.select element does.
Actually you can't use CSS selectors with the Ext.fly method. I think you are confused with the Ext.select method, which returns a CompositeElementLite instance containing an array of all elements conforming to the specified CSS selector. It lets you perform operations on a collection of elements as if you are using a single element. This is very close to what the jQuery $('.some-selector') provides you and works by iterating over the elements array and swapping the DOMElement pointer on an internal Flyweight instance right before it executes the operation on that Flyweight, and thus performing the operation on each element.
Actually you can't use CSS selectors with the Ext.fly method. I think you are confused with the Ext.select method, which returns a CompositeElementLite instance containing an array of all elements conforming to the specified CSS selector. It lets you perform operations on a collection of elements as if you are using a single element. This is very close to what the jQuery $('.some-selector') provides you and works by iterating over the elements array and swapping the DOMElement pointer on an internal Flyweight instance right before it executes the operation on that Flyweight, and thus performing the operation on each element.