Jerry,
The IB line charts vary in their resolution, depending upon the total amount of time covered by the chart. Intraday charts spanning a small part of the day cover prices much more frequently than once per minute, while intraday charts covering the entire RTH do display only one price per minute or so. Your QT approach is superior, because you allow display of all available data, so that all the highs and lows and zig-zags are displayed, up to the extent physically permitted by the graphics resolution of the user's system.
IB line charts do not display closing prices from each minute or other time interval, as both you and I had assumed; I learned from an IB employee, in this thread, that IB actually uses a VWAP or TWAP to determine the average price displayed for each minute or other time interval. This type of chart can be duplicated by your QT by using moving averages.