Consider that Tone on the piano is created by the balance of Speed (how fast you strike the key) and Weight (how much mass you bring to the key). You could think of the quality of sound being determined more by the speed and the volume more by the weight. Well, at this point of our technology digital instruments cannot yet accurately register (and therefore replicate) that subtlety of Tone, or dynamic graduation though they are definately getting closer. A well-maintained console or upright can do this,and a grand piano does this even better.
So, yes, you will learn more about the sound and tone youre creating on a real piano. For some piano students this can make the difference between being excited about practicing or not. Many students find a way to balance their keyboard time with real pianos found in schools, churches, friends,family, or inexpensive practice studios. (The vast majority of the pianos at any given time are not being used!) And many students find lots of enjoyment playing a modern digital piano.
Nowadays there are keyboards that not only features a nice weighted action like a real piano but offer a graduated action that replicates the sense of lower notes feeling heavier and higher ones feeling lighter. Models that come with built-in speakers will also give the player a sense of the sound vibrating through your body, just like an acoustic piano. Yamaha has several models that have both of these features.
Digital keyboards DO have important advantages over traditional pianos: they never go out of tune, can be used with headphones (very important for apartment dwellers or parents of youngsters), take up very little floor space, are generally very portable, offer a wide variety of sounds, and can easily be integrated with a computer set-up. (These last two items are very useful for composing and songwriting). And for a variety of reasons, some performers only use a keyboard rather than a piano.
The bottom line is that you can make consistent progress with your music using either type of instrument!