That bike has what is called a compact frame design. Traditional bike frames come in many different sizes, typically going up by one centimeter or half-inch increments. About 10-15 years ago most major bike manufacturers started making compact frame designs with sloping top tubes. These typically come in a smaller range of sizes (extra small, small, medium, large, extra large). This saves the bike company from having to make as many sizes of the bike as they used to. With compact frames you just have to make sure the bike is an approximate fit for you. If you need to "tweak" the sizing, then you adjust the seat post, handlebar stem, etc.