I actually agree that Corel are being scummy here, but you can enforce look and feel without patenting sliders for zoom and tabbed toolbars.
An observation: Corel copied the awful bits (gloss and low contrast blue) as well as the good (organising the toolbars using tabs). If they had only copied the good stuff, they would have come up with the look of Microsoft Office 2010 and perhaps had a better commercial opportunity.
People seem to be missing the point that the patent isn't for 'sliders' but, as the article points out, that very specific design of slider. Not the functionality. TBH, I think it looks pretty horrible, so no great loss here.
An observation: Corel copied the awful bits (gloss and low contrast blue) as well as the good (organising the toolbars using tabs). If they had only copied the good stuff, they would have come up with the look of Microsoft Office 2010 and perhaps had a better commercial opportunity.