They don't necessarily need to do anything with the packet then -- they could always pass a copy to cold storage, and then crunch the bits at their leisure in a massive data center.
A) this is probably true to an extent.
B) slurping everything to disk is impractical, and no one has that much storage, so you're back to parsing and deciding at the boundary. This "leisure" time doesn't ever happen when you save everything all the time.
C) this point seems to contradict the various claims of reasonable network maintenance I've seen; if it's trash you want to drop, you want to drop it on the floor not on your disk. If you're keeping actual traffic rather than just summaries of traffic, you're not doing reasonable network maintenance.
