This is confusing the fuck out me.
Under perfect usage, they are about 98% effective (source).
Unless I've greatly misunderstood things, perfect usage means that a given condom is used once, hasn't been torn/ripped, the right size was used, and was properly put on. In testing, condoms are filled with 1+ liters of water and stand up to the pressure just fine without leaking.
EDIT: The only thing that makes sense here is that 'perfect use' only refers to humans doing their part correctly, but the condom not being manufactured quite right and breaking. Is this correct? It's not entirely clear what the definition of 'perfect use' is.
Perfect use = humans doing their part correctly, ignoring manufacturing failures.
The statistics are for 1-year failure rates.
Microtears are not a significant factor, like I suspected.