Time and Newsweek poll data

Time and Newsweek are reporting a post-convention bounce for President Bush greater than 10%. That seems really high to me. Rasmussen Reports agrees with me. They calculated a bounce of 4--5%. So why the big difference? According to Rasmussen:

Those polls [Time and Newsweek] appear to have the mirror image problem of a Los Angeles Times poll in June reportedly showing Kerry with a huge lead. That LA Times survey included too many Democrats in their sample. Today, it seems likely that Time and Newsweek included too many Republicans. Time reports that Republicans will vote for Bush by an 89% to 9% margin; Democrats for Kerry by an 80% to 9% margin; and, unaffiliated voters for Bush 43% to 39%. Four years ago, 35% of voters were Republicans, 39% were Democrats, and the rest were unaffiliated. If you apply those percentages to the Time internals, you find Bush up by about 3 percentage points. If you do the same with the Newsweek internal numbers, you find Bush with a six point lead. Those results are very close to the Rasmussen Reports data (excluding the Saturday sample). All of this leads me to conclude that the President is currently ahead by 4 or 5 percentage points. As always, it's useful to use common sense when reviewing poll data. If a poll suggests that 10 or 20 percent of Americans are changing their mind on a regular basis, it should be viewed with caution. Most of the time, you will find that the partisan mix of the polling sample is  changing more than the actual perceptions of voters.

Given this seemingly basic information ("common sense" as Rasmussen puts it), what is the reason for the inflated Time and Newsweek results? Is it partisan bias? Or perhaps the simple desire to report a large number rather than a small one? Perhaps it is due to simple ignorance (how many math courses do journalists have to take?)? This is just one more in a steady flow of instances which have caused me to view Time, Newsweek, and other such pulp as "fringe" news rather than mainstream sources. Speaking of pulp, the Deseret News on Friday ran a headline (front page, it may have been) which read "Bush's Agenda for America Cheered." What kind of a headline is that? They might as well have put "Get with the Winning Team!" or "Everybody Loves Our Hero Bush! Yay!" Since when is it "news" that the nominee is cheered at his own party's convention? Stupid newspaper garbage. Nobody knows what objectivity looks like any more.