What the OP fails to understand is that the very bottom of the LBS bike range is still somewhat above the very top of Department store bike range. Also, the LBS is far more likely to assemble and adjust the bike properly.
Go to Target or Wal-Mart and ask the sales person in the bike department about recommended seat height and then do the same at a bike shop. Let me know who gives the more useful information.
I've worked on low end bike shop bikes and tried to work on DS bikes. The differences are clearly apparent.