What you are saying is the same thing I was thinking until I became buried in this issue.
When you start looking at elections, it is amazing (I'm stunned frankly) at how much comes up. Every freaking state (and sometimes at a county level) have different rules. And the applications that are used to run elections need to be configurable by civil servants who may or may not have a high degree of IT familiarity.
There are a couple points to consider.
Scanned ballots are probably a lot easier to deal with, in terms of the tabulation software, and thankfully offer a paper document that can be re-scanned if necessary. That's a good thing.
But there is an interface that allows the elections staff to configure the machine/ballots for different races, with X number of candidates, can you vote for one (only) or for more than one... Then you have to accomodate propositions and such.
The scanner needs to be configured to know where to "look for" the voters mark, and what the marks indicate, based on the layout of any particular election's ballot. (You should have seen the one for the CA Recall - it was brutal.) The software has to know if an undervote or an overvote has occurred.
So it actually becomes a robust application to configure the scanner, count/verify the ballots at the precinct, and finally consolidate the totals at the county level.
Yeah, not rocket science, but also not as straight-forward as it would seem on its face.
Then we get to the touch screen systems. The Diebold system runs on Windows CE. The user has to be able to "paint" the screen for each election, defining different races and everything else, configure how each race works (as in 1 or more votes are valid). My impression is that this makes for a very complex application when done properly, and (at least) Diebold has left "properly" wide open for curiosity and challenge...
Speaking of CE, Jim March discovered that Diebold was hiding the fact that it was not COTS (Commercial Out of The box Software), and they appear to have acted to avoid having that software certified. In case your are unfamiliar with Jim, he is a California lobbyist for "Concealed Carry Permits" - not exactly what you would call a flaming liberal - he is a staunch conservative and a good friend. Here is a page in his site where he discusses the CE problem http://www.equalccw.com/sscomments2.html
So anyhow, I get your point, but the software simply is not simple... Here is a list of bugs fixed in just one release of their code: http://www.countthevote.org/buglist.htm
BTW, if you have not followed the Diebold e-mail discussion, check this series of thread at www.blackboxvoting.org
http://tinyurl.com/2rzqv
The big difference with scanned ballots versus touchscreen is that most of the touchscreens presently have no printed "ballot" or anything else that serves for a recount. And without that, elections are getting hosed: not a theory, but a real and growing fact.
Please help us stop this threat to democracy.