That doesn't really show bias. It does show how question wording can effect results.
Intentionally using an alternative method when you know what results the method will produce, and those results are anti-Obama is bias.
The link also points out that Rasmussen's use of likely voters skews the results to the right. Rasmussen knows this.
If bias is not the motive, tell us what the motive is. There has to be a reason that you abandon a standard practice and switch to a non-standard one. Give me a plausible reason or reasons that Rasmussen would do this.
Rasmussen has always used this method though. It's not new. They used the same survey method while Bush was President.