I guess I could be more specific about changing the rep ranges. Traditional periodization (IIRC, LoL) involves basically starting w/ lighter weights and more volume (basically, more hypertrophy focused) . . . then you transition into more of a strength phase where you're lifting heavier weights and doing fewer reps . . . and then you "convert" that new strength and size into power and build up to a new max single. So by the end, you're doing very little volume but using gut-busting weights whereas at the beginning you were doing lots of volume w/ moderate weight.
One problem w/ this approach is, there seems to be little "carry over" from one rep range to the next (e.g., improving your best set of 15 won't really improve your best set of 3). So while the goal is to hit a big single, why are you messing around w/ 10s? Another problem is that as you move from one rep range to the next, you're basically dropping the old rep range. So even if you get some adaptations, you may lose them b/c you'll go for several weeks w/out ever hitting them again. For example, let's say you work sets of 10 in weeks 1 & 2, well by weeks 7 & 8, you're no longer doing 10s and there's a good possibility those adaptations disappear between weeks 2 and 8.
So those are some problems w/ rotating rep ranges in a weekly block fashion. The 5x5 as set out on madcow's site has you rotating DURING the week a little bit, in that you're hitting a heavy triple on one day and a heavy 5 on another (or multiple sets of 5). Plus, yo'ure doing some backoff sets so you're keeping some adaptations from the higher rep range each week. IMO, it's the best of all worlds really. But, I'd have to look at the BFS exactly to see how they rotate the reps and how they structure it both within each week and across several weeks. It's a good program, from what I've heard. Again: logical progressive training w/ non-stupid lifts.