I would imagine, and this is just a guess, that the variable nature of electronica and dance music has to do with the fact that no-one is actually playing an instrument and that it is computer generated in non-real time. So as long as you keep to a pattern, everything fits. Not that I am knocking that, but when a human is creating the sounds live then I have found they tend to follow their heatbeat in the abscence of anything else to sync on. There is, of course, variance whenever human beings play anything but when you tap it out with a metronome you do see the centers in increments of 15 and typically 30 (sixteenth notes at 15 BPM = eighth notes at 30 BPM = quarter notes at 60 BPM, etc...). 120 BPM is what most drummers lock into when on autopilot.

The reason I noticed this in the first place was analyizing the walls I was hitting in my own playing. My friend explained the heartbeat theory to me and I have found it generally fits with the other musicians that I know. This also only applies when you are playng "naturally". People like jazz guitarists who try to break all the rules will avoid what feels simple or cliche, but they are making a conscious effort to fight against what feels relaxed and expected.

That is also why most music is written around intervals of 60 PBM. If you hand a musician their instrument of choice and just have them noodle around they almost always play at some multiple of 60 BPM (90, 120, 180, 240). I can play scales all day long with 16th notes at 60, 75, 90 and 120 BPM, but some odd interval close to those numbers like 72 or 87 and I will be lucky to get a run of 10 in a row. My brother tends to hang around 145 which has always puzzled me, then I found out his resting heart rate is 72 BPM. It is like the body uses itself as a metronome. Pretty cool actually and it also explains why bands tend to play faster live as the set goes on.

I thought of the capacitor/battery issue as well when laptops were mentioned but who says that you have to power it up with the original components in place. Just put a circuit board enclosed in as hermetically sealed ESD bag in the capsule with a BOM, schematics, and parts locater and let them build the computer when they open it up. If you are feeling really generous give them assembly instructions as well. I might even include a little leaded solder for posterities sake.
There are classic guitar amps that were built in the 50s that are still in use today. The tubes, caps, pots, and other components have been replaced over time but the same basic wiring is there.
There will be components that can stand-in for the ones that are obsolete. We are only talking digital here, 5V is 5V you don't "color" a digital signal by changing the material that a component is made from. Now if the data was stored on a metal stamped DVD or CD and sealed up it would probably stand a decent chance. It might be a little labor intensive but so is digging up and opening a big steel capsule that has been welded shut 25 years earlier and they will also get to build an "old-school" computer in the process.