On falling Mac sales and the lack of refreshes

From Joe Rossignol, writing for MacRumors:

The latest numbers from market research firm IDC reveal that Mac sales experienced a slight year-over-year decline in the second quarter, dropping to 4.4 million from 4.8 million during the year-ago period.

Nick Heer, writing for Pixel Envy:

Apple’s sales decline is an 8.3% reduction compared to the year-ago quarter. Given that the most recent Macintosh news — the discontinuation of the Thunderbolt Display notwithstanding — was a spec bump of the MacBook, this is completely unsurprising. MacRumors’ own buyers’ guide shows a “Don’t Buy” indicator below every Mac except the MacBook.

And:

I look at models like the iMac and the MacBook and I see investment in the Macintosh. They’re beautiful and capable machines. But then I gaze over the rest of the lineup, and I’m disheartened.

I get the sense, from the last six months of rumors, that a new MacBook Pro is coming soon. But that coming soon has been the case for a while now. And I have not heard anything about a new Mac Pro.

Nick Heer again:

The pro Macintosh situation is so dire that some designers and developers, like Mike Rundle and Sebastiaan de With, have opted to deal with the moderate hassle of building a “hackintosh” in order to get the performance they need for their work.

What is the story here? Is the Mac space too small, revenue-wise, for Apple to go to the trouble of a new product launch? Is something else causing this lack of new models?