IIRC FLAC's compression complexity is a lot higher than its decompression (which is generally the way you want it for playing back on dumb devices), and the level is just the amount of computation you want it to take to try and make the file as small as possible while still being 100% bit-perfect. It's like having the equation 1+2+3+2+1=9. 0 is stored as 1+2+3+2+1 and level 8 is stored as just 9 but it took more work to get to that result.
You can analogize frames on a CD to sectors on a disc. It's just a compartment for X number of bits in the track. I believe iTunes just rips the same frames again and compares them. If equal, move on. dBpoweramp appears to go into the real secure mode that EAC has, to ensure it really is getting the right bits. If you don't like this about dBpoweramp you can change the setting to just do Burst rips or you can change the secure settings so that the maximum re-reads is reduced from the default of 34 times.
BTW I just noticed R13.2 is out now, so it might be worth downloading the upgrade
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