This is why video game companies hire more artists than programmers. Counting frames is often not productive though, cut-out animations (which PvZ appears to be using) allow artists to render many frames from one base illustration and some extra work. They're not necessarily easy but they're often a large time savings over frame by frame.
Yes, my idea behind it is generally draw a sprite, copy it into a new frame, move some parts of it, then reconnect and clean up the ugliness that results from an arm being completely disconnected from a shift in the rest of the image.
According to a pixel artist friend of mine, all the companies he's worked for using those types of anims will build a proprietary tool that essentially works like Flash in a pure-bitmap context; tweening, scaling, rotation, and bitmap cutouts(e.g. parts that bulge and bounce, like the belly of a fat character, simply reuse an area of the sprite and layer it on top). These tools are used for menu layouts and level design as well as sprites.