Essentially it's a throwback to a simpler age when mountain bikes had no suspension and used steel frames. An old skool mountain bike is a wonderful thing, with just a change of tyres it'll cope with just about any terrain you might throw it at, commuter during the week and proper off road trails at the weekend. 'Hybrids' can't do both in spite of what the marketing folks claim because they cannot take a fat, high volume knobbly off road tyre.
It doesn't have a light frame by modern standards, steel frames are (usually) heavier than aluminum frames. But. Steel frames are cheaper to produce which means that for a given price-point you'll get better parts than you would on an alu frame, they are easier to repair and some people claim, myself included, believe that the ride quality is better.
When you consider that a complete bike at this price point weighs between 27 and 30lbs, and the frame alone weighs between 4 and 7lbs, the frame weight isn't a huge factor. My Mrs's bike has a similar (Kona) frame which has seen several years of gradual upgrades and weighs about 25lbs all up. Which is a pretty good weight for a mountain bike.
With a change of tyres to some 1.3 or 1.5in slicks it'll cope very well with a 15 mile commute.
It's what I designed it for!
Watch out for the 2008 model, they ruined it by making it a 'twenty niner' and somehow made it heavier.