solivagant: the point is that if, for example, you are squatting with 100lbs for your 15RM and you choose to increment towards your 15RM in steps of 10lbs, then you are using steps of 10% of your RM load. If Steve is squatting with 400lb for 15RM (just a guess, but he might be cos he's strong as an ox!) and is using 20lb increments to get to it, then he is using steps of only 5% of his RM load.
This is why it is quite a good idea to use %ages to figure out your increments (5-8% being quite a useful amount), though most of the time, simply using 5lb or 10lb increments is good enough (and easier to figure out too). Use 10lbs for your big lifts, like squats and deads, and 5lbs for your lighter lifts. Watch out with dumbells - only add half the total increment to each one.
One other useful pointer is to use a starting weight that is around 60-70% of your RM load. However, using your example, I would use a progression more like this:
Workout 1 (Week 1, Monday)-75lbs
Workout 2 (Week 1, Wednesday)-80lbs
Workout 3 (Week 1, Friday)-85lbs
Workout 4 (Week 2, Monday)-90lbs
Workout 5 (Week 2, Wednesday)-95lbs
Workout 6 (Week 2, Friday)- 100lbs
... because, if I started with 65lbs it might be awkward to find weights for the progression! Eg. 65, 72, 79, 86, 93, 100 (7lb increments - 3.5lbs either side of a barbell).
To avoid that problem you could do something like this: 65,75,85,90,95,100
I think Bryan has mentioned that it is a good idea to make the load increments larger rather than smaller, so make them as large as you can without starting out with a weight that is much below 65% of your RM. Make the increments practical so you don't get bogged down in the detail. Ultimately, it's the progression over the whole cycle that matters most. Hope that helps and doesn't confuse you more.