I believe one of the aspects that makes it different in the US is that on election day, there isn't only one thing to vote for. There's the President, a Senator, a Congressman, a Judge, local public transports directors, etc. and a bunch of propositions. And that's different from one county to the next, from one state to the other.
I suppose that's part of what made it interesting to look into computerized voting machines.
To make sure nobody takes puts e.g. national slips in all three envelopes there's a small cutout at the edge of the envelope that shows the color of the slip inside without revealing the vote.
Or you could look at land size. Sweden's size: 449,964 km2 or 173,732sq mi. United States size: 9,826,630 km² or 3,794,066 sq mi. Have to transmit the data somehow - its not like you can drive the ballots across the US to one central point in under a few hours. So why not do it one at a time as they're cast electronically? Assuming it's done properly at least.
"Why not do it electronically, assuming it's done properly": that's just the problem - it can't be done properly.
Using a computer system is not very compatible with the basic principles of voting:
* Each person gets one vote, and only one vote * It must be impossible to figure out what some specific person voted for
Computers are good for the first part, given infrastructure to support it (provide each person with a way to identify themselves to the computer - smart card and biometrics maybe). They suck at the second part, though.
In Sweden we have a simple system: paper slips with party names printed (or written) on them. You select someone to vote for, put your paper slip in an envelope and drop that in a box after someone checks your identity and ticks you off in a list of voters.
After everyone has voted, the box is emptied, the envelopes are opened (checking that each one contains a single vote) and the slips are counted manually. Results are reported to the voting comission (or whatever they're called) who sum the votes and then it's all done. We have the results a few hours after voting is finished.
In the US the same system should work well, I don't really understand what the whole voting machine thing is good for. It's not like there's an election every two weeks, computerized voting machines will probably be used maybe two times in their lifetime. A waste of resources!