Part of the problem is Politifact's structure. A group of researchers will investigate an issue then an editorial rates the result on a scale ranging from "true" to "pants on fire". More recently, Politifact has added state affiliates which may or may not adhere to the same standard.
Here is an example of one claim recently rated by Politifact. During his speech, Paul Ryan referred to an auto plant in Janesville, Wisconsin. He said that Obama pledged to keep the plant open during a campaign stop in 2008 but the plant is now closed.
This is what Obama said:
And I believe that if our government is there to support you, and give you the assistance you need to re-tool and make this transition, that this plant will be here for another hundred years. The question is not whether a clean energy economy is in our future, it's where it will thrive. I want it to thrive right here in the United States of America; right here in Wisconsin; and that's the future I'll fight for as your president.
GM had already warned that the plant might close because of sagging SUV sales. Does this sound like a promise to use government funds to retool the plant to produce "clean energy" cars? It kinds of sounds like it to me.
The plant closed December 23, 2008, less than a month before Obama took office. Does that let him off the hook for keeping it open or was he still obligated to reopen and retool the plant at government expense?
Considering that the stimulus included funds for just such projects and Obama was personally involved in deciding which plants would close and which ones would stay open or reopen, the Janesville workers would seem to have a reasonable expectation that their plant would reopen. It didn't happen.
None of this is in dispute. Most of these details came from Politifact. This is where the editorial board come in. Did Obama make a promise that he should be held to or was he just making a broad statement of belief that had nothing to do with the future of that actual plant? The editorial board went with the latter.
So, did Obama break his promise? Not according to Politifact. Because Obama gave the impression that he would keep the plant open instead of using the words, "I pinky-swear that this plant will not close," Politifact let him off the hook and rated Ryan's statement false.
This is where conservatives get upset with Politifact. A different editor might have noted that Obama purposely left the workers with the impression that he would personally do everything he could to keep the plant open and further note that the stimulus and the GM bankruptcy gave Obama direct influence over which plants would stay open. By that standard, Ryan's statement would have been rated "mostly true".
On many rulings there is no question about the truth. For example, Obama's deputy campaign manager, Stephanie Cutter claimed that the Obama economy created more jobs than the Reagan economy. It doesn't matter how you twist the figures this just isn't so and Cutter earned a "false" rating. Even there, they would have been justified in giving her a "pants on fire" rating. As their analysis mentions, when you take the size of the economy into account then Reagan increased the workforce by 11% compared to Obama's 4% during the comparable period. If you figuring it from the end of the recession instead of the low point of employment then Reagan's gains were 13% and Obama's 3%.
The subjectiveness of the ratings is what drive conservatives crazy.