Obama's opening statement at this evening's press conference, delivered no doubt with the help of a teleprompter, sounded smoother and more polished than his real-time answers through the rest of the event.
The same is true for any public figure who has learned to use a teleprompter (harder than it seems) and whose teleprompter-ready material suits his or her natural speaking style. It sounds smoother than extemporized speech because it should be smoother. People don't naturally speak in parsed and polished sentences, even eloquent people. When we are listening to what we know is spontaneous rather than scripted speech, we listen in a different way -- we listen past grammatical glitches, repetitions, and other things that would be "flaws" on a printed page or in a formal oration. If you don't believe me, look back for any extemporized performance that was judged to be riveting by audiences in real time. (A campaign rally, a TV interview, a debate, the closing argument in a trial.) If you then read a word-by-word transcript, it will look like a mess.
The important point with Obama is that the content, command of fact and concept, and overall intelligence of his extemporized answers matched that of the scripted presentation. That could not have been so if he were teleprompter-dependent. For example: by the end of his term, George W. Bush had become quite effective in delivering a formal speech. His interview- and press conference performance if anything deteriorated through his time in office.
The whole "Obama can't talk on his own" concept is bizarre, given his performance through two years of stump speeches and debates during the campaign. But it seems to have gotten so much credence in the right-wing world that it is worth addressing head on.