iOS developer here, see the same thing with any article writing positively about an Apple product
http://hnrankings.info/4849090/
Microsoft mocks Internet Explorer haters in new ad
They should be thankful the dev community is giving IE10 a go and actually being encouraging to some extent.
Why should propaganda necessarily be something we see promoted on HN? At last previous MS ads apologised for the 1000s of hours debugging poor IE bugs.
It's meant for bad links. Spam and off-topic articles are included, but that is not its exclusive use. For example, a post about how much the author hates gay startup founders is more on-topic than a lot of stuff that gets posted here, but is nonetheless inappropriate on numerous levels.
I don't know if I would flag a news story about a Microsoft ad campaign, but I'd probably at least consider it, because those are not generally very intellectually stimulating.