The main reason for redundancy is because NASA can't send someone out to fix the probe/satellite, so the hardware has to be designed to work flawlessly for decades. Astronauts use consumer laptops just fine on the shuttle and ISS, and I doubt most of those even have ECC RAM.
Airplane avionics aren't radiation-hardened, but they work fine at altitude where the incidence of cosmic rays is about 1/4th that in space. Planes aren't dropping out of the sky from bit flips. People don't get tons of parity or ECC errors on their laptops while flying. Based on all this, I think the threat of cosmic rays is vastly overstated.
Worse yet, if your probe's OS crashes at the wrong time it could lead to loss of the probe or missing out on a lot of data that would otherwise have been gathered. If a probe's electronic brain crashes due to cosmic rays and goes into a "safe" state it may fail to maintain attitude control, potentially pointing its solar arrays away from the Sun and/or its high gain antenna away from Earth. This can lead to "bad things" such as the probe draining its batteries and dying before controllers have a chance to fix it (this has happened quite frequently in the past, though not always due to cosmic rays). Worse, the probe could reset during a critical course correction manouver, end up failing to go into orbit around a target planet, burning up in a planet's atmosphere, or merely ending up in the wrong location on the wrong trajectory.
Avionics systems use ECC memory and other techniques to avoid being impacted by cosmic rays causing single event upsets. As far as parity and ECC errors on laptops, I don't believe ECC ram is common on laptops.
That being said, this particular article uses a gross overestimate of SEUs for memory, which is really only applicable if your 4GB of RAM fills an entire room in multiple full sized racks (the studies he bases these figures on come from the 80s and the author fails to adjust for physical size when extrapolating to modern memory sizes).
Do any laptops support ECC RAM? Lots of machines will run with ECC RAM but only a few can perform SECDED (single error correction, double error detection). I had SECDED in my previous desktop and the machine seemed more stable than the one I had before. Here's Daniel Bernstein's rant on the subject: http://cr.yp.to/hardware/ecc.html
Microsoft's datacenters have a straightforward policy for dealing with software errors: first restart the service, if that doesn't fix it then restart the OS, and if that doesn't fix it then swap out the machine.
Airplane avionics aren't radiation-hardened, but they work fine at altitude where the incidence of cosmic rays is about 1/4th that in space. Planes aren't dropping out of the sky from bit flips. People don't get tons of parity or ECC errors on their laptops while flying. Based on all this, I think the threat of cosmic rays is vastly overstated.