While the Master Collection is 'only' $800 for students that is an up front fee that many cannot choke down in one lump sum. Additionally that one time fee does not grant the 'owner' of the software the ability to upgrade. Adobe upgrades their software about every year and a half.
As for the student cost, it's only $29.99 after the special offer is over. Not a 'Full Whack' as was said. Just $10 more. Still within a students budget, where dropping $800 each year is typically not.
Many students, and many designers, require more than one of Adobe's products. For a web developer you would need at least Photoshop, Dreamweaver, Flash, Edge, Muse, and Illustrator in your arsenal just to be competitive. A video professional would use Premiere, After Effects, Photoshop, Encore, etc. Even a graphic designer uses Photoshop, Illustrator, InDesign and others just to be successful.
It's quite short sighted for a professional to rely on only one main program. In today's design field you would be outdated very quickly if you relied on one program that you didn't upgrade every iteration, or every other at least.
'Owning' your version of CS6 is all well and good, until you are behind a version or two and a client requires you to use a feature or deliver a project in the newest version. At the very least you can be embarrassed and force them to support your old version, or you can dump the funds at that time and install all the upgrades then and there just to save face. If you think this doesn't happen then you are not a professional in the field. Happens all the time when you use Flash, After Effects, Premiere, and InDesign. MAYBE you can get away with Photoshop or Illustrator if you happen to only deliver final work that a client does not integrate into other workflows.
Having been an Adobe user for the past 20+ years, as well as many other software developers, I'm very happy to have a monthly fee of $49.95 a month rather than dumping thousands of dollars every couple of years. And yes, I have used nearly every piece of software that Adobe makes throughout my career.