Take note of the component Fat - amount per 100g. Some can be 100-150% higher than others.
Just FYI, it may not be very good for adults to take too much fat but it is a different case for babies. Babies need a high fat diet as it is essential for brain development and body nutrition. Even young children would be well off with a high fat diet as their brains are still developing. Of course, there are different types of fat. Saturated fat is not good. Get the good fats into your babies and children... they will become smarter... hehe...
As for the difference in fat content of different formulas... perhaps those with higher fat is to help babies on the thin side to gain weight?