In my household there are two iPads, two Mac's and three PC's (I am a professional software developer, and my girlfriend loooves her apple products). So I have used all of them pretty extensively.
The reason I have not used my iPad for serious work (As in, developing software, writing my documents, checking e-mails) has nothing at all to do with the storage available on it.
With my PC (Or even a Mac) I can do all the stuff I want to do on a Mac (given that I can replace the OS on the Mac with linux, as Mac OS is a bit too much of a (my personal opinion remember) toy for serious work other than writing, photoshop or any other artsy productivity). And I can do it all on my PC as well.
The reason the iPad pretty much solely as a reading device these days is simple. Its form factor and user interface suck (again, only my opinion). It is when I can install any software I want on it without being held back by the app store. The day it becomes professional is when I can load any music, files or documents onto it without the need of secondary software (iTunes). It is when I can actually do work on the iPad without feeling constrained by the display and size of the device.
It is when the device and its operating system stop feeling like a "gosh apple is cool" kind of advertisement/toy/gimmick.
That blog post read like the rant of a overzealous apple fan fawning over the newest apple product. What about extra space changes it towards being a professional-grade machine today when we have almost unlimited cloud storage at our disposal?
Yeah, I don't get it either. I find OS X is my preferred environment for hardcore dev; I have the best of many worlds - terminal, multiple desktops, browsers, text editors, word processors, spreadsheets, email - I consider that pretty serious work.
At least in my area, people start out programming on a Mac, get tired of the endless workarounds they need to do the most basic Unix development, then just set up a Linux VM. Then, when it's time for a new laptop, they just buy a Thinkpad.