It is, but the original idea has already been distorted by two-plus centuries of evolution.
The House, for instance, was originally supposed to be extremely close to the people; the first Representatives served districts that had just 30,000 people each. That's roughly the same number of people as live today in Butte, Montana, or Fairbanks, Alaska. A district small enough that everybody could know their Representative personally.
As the country grew, though, the House chamber started to get crowded. In the first Congress, the House had all of 65 members; by the election of 1900, there were 386. And this had practical consequences -- all those people had to squeeze into one room. People started to worry that further growth would make it unmanageably large.
So in 1911 Congress passed a law, the Apportionment Act of 1911 (http://en.wikipedia.org/wiki/Apportionment_Act_of_1911), that essentially waved a magic wand and said that from that point on the House would have exactly 435 members, and changes in population would be dealt with by shuffling seats from shrinking states to growing ones rather than by adding new seats. That's more or less the system we have today.
The problem is that, as the country kept on growing, each of those 435 seats had to represent more and more people. Today each one contains something like 700,000 people. That's more people in one district than any of the original thirteen states had in their entire state. (Virginia, the largest state in 1790, had just 455,000 free citizens.) Which sort of demolished the idea that districts would be small enough for everyone to know their Representative -- today's House members are even more distant from their communities than the first Senators were.
(Which is why there are occasionally calls to radically expand the size of the House; see http://www.democracyjournal.org/8/6587.php for an example.)