Short Answer: Your instinct was right, 4 sets will tone you faster.
yeah, it matters. There are basically two different goals to weightlifting - aerobic and anaerobic respiration in the muscle cells. Aerobic is what you get from light weight, long duration output - makes you sweat, like running. Anaerobic is slower, heavier weight, shorter sets. You may see huge guys in the gym doing short sets of tons of weight, resting 2-3 minutes between sets, hardly sweating - that's what they're doing.
There's a million opinions on exactly how many reps per set constitutes aerobic or anaerobic, and it varies by body part (higher set counts on lower body muscles than upper body). The best flexible rule is if you're sweating, you're doing aerobic work. Numerically, if you're doing sets of 10, you're working in the aerobic area, you're sculpting, toning - not building, muscle. It means that over time you'll burn away lots of fat in that area of the muscle and it will show more, be more shapely and toned, but not extensively grow in size.
As far as number of sets, it depends on a few things. Let's say you're doing a chest workout. If you intend to do more than just 1 lift in this chest workout, like you intend to do dumbbell presses, the pec fly machine, and decline bench (just as an example), then you should be more concerned with the total
number of sets you do than the number of sets of each exercise, because in general you're targeting one muscle group - the chest. Now the caveat that some people will point out is that each of those exercises specifically
targets a different part
of the chest (upper, lower, etc) but in general, each of those exercises relies on the whole chest. All that changes is which muscle is the isolation muscle and which are the control muscles, but they're all used in general.
The other question is how long you're resting between sets. Typically guys that are trying to get big, as I already mentioned, rest 2-3 minutes between sets because it allows the muscle to recover about as much as it possibly can, and then you go again and fatigue it all the way down to exhaustion all over again. In the case of trying to work aerobically, you don't want to rest that long - because you want to sweat. You want to rest 30-60 seconds between lifts, closer to the 30 side.
The reason this effects how many sets you want to do is because if you're only resting 30s between sets, you don't need to do as many before your muscles will totally burn out, and that's the goal. The only reason you might want to do more than 3 sets (with your toning goal in mind), is if you are resting for longer periods of time in between sets than 30s, but doing longer sets (say 12 or 15 reps), and want to accomplish some measure of growth towards the end of your sets. Sort of like hybridizing the workout between aerobic and anaerobic. If that's not your goal, then you don't really NEED to do more than 3 sets.
Keep in mind you should always be going to exhaustion, the question is whether you're lifting a weight where exhaustion means 10 reps, or whether it means 6 reps. The 6 reps is where you'll get growth, the 10 is where you'll get toning.