I've been using Fireworks for years, back to Macromedia Fireworks 4. It's much better/faster than Photoshop for web design (rounded square corners come to mind). If you work on a Mac, consider Sketch by Bohemian Coding : http://www.bohemiancoding.com/sketch/ It's a great app, is updated very frequently and has come a very long way and could almost be seen as already superior to Fireworks CS6 in most ways.
The best way I've found to make rounded corners in Photoshop is by using the round rectangle vector tool. It's relatively new, so you may not have tried it.
It's not the creation of rounded rectangles. It's being able to change the radius afterwards (which Photoshop can't do). Also, if you want to change the size of the rectangle later in Photoshop, without distorting the corners, it's not easy -- you have to subselect specific control points, and then move them.
It's not impossible in Photoshop, it's just that modifying rounded rectangles is a huge pain.