Helvetica can't do everything
Despite its grand reputation, Helvetica can't do everything. It works well in big sizes, but it can be really weak in small sizes. Shapes like 'C' and 'S' curl back into themselves, leaving tight "apertures"--the channels of white between a letter's interior and exterior. So each shape halts the eye again and again, rather than ushering it along the line. The lowercase 'e,' the most common letter in English and many other languages, takes an especially unobliging form. These and other letters can be a pixel away from being some other letter, and we're left to deal with flickers of doubt as we read.
Lucida Grande presents open apertures, inviting the eye to move along sideways through the text. It has worked really well--for years, and for good reason. For any text, but particularly in interfaces, our eyes need typefaces that cooperate rather than resist. A super-sharp Retina Display might help, but the real issue is the human eye, and I haven't heard of any upgrades on the way.