What is the difference between the BMW 2006 325i and the 2007 328i?

I am new to BMW, so originally I thought that there were only 2 in the 3 series (the 325, and the 330 with the larger engine). Now they have the 328i this year, and I don't see a 325. What's the method behind their number system,

What is the difference between the BMW 2006 325i and the 2007 328i?mcaffee

Per wikipedia:

US models only!!

2006 325i - 3.0 L I6, 215 hp. Sedan Only.

2006 325xi - 3.0 L I6, 215 hp. Sedan and Sport Wagon available.

2006 330i - 3.0 L I6, 255 hp. Sedan Only.

2006 330xi - 3.0 L I6, 255 hp. Sedan Only.

2007- 328i - 3.0 L I6, 230 hp. Sedan, Sport Wagon, Coupe, and Convertible available.

2007- 328xi - 3.0 L I6, 230 hp. Sedan, Sport Wagon, and Coupe available.

2007- 335i - 3.0 L I6, 300 hp. Sedan, Coupe and Convertible available.

2008- 335xi - 3.0 L I6, 300 hp. Sedan Only.

2008- M3 - 4.0 L V8, 420 hp. Coupe

2009- M3 - 4.0 L V8, 420 hp. Convertible

Looks like the only difference would be in head design, internal parts, exhaust restriction and tuning giving more horsepower to the 328.

Typically the 3 is the series and the 25, 28, 30 is the displacment in Liters. 2.5 L, 2.8 L, 3.0 L.

However in this case, there is no actual difference in displacement as there usually is between BMW's. Appears that they are using the same block for all the engines from the 325-335.