On iOS when you type a string of characters and the spell correction shows up, you need to actively cancel the suggestion if you don't want it.
The same goes for a searching on Google and Yahoo which informs user that they are showing results for X with the option to search for the possibly misspelled phrase.
On Bing, things are a little different. They say including results for X with the option to search only for the possibly misspelled phrase.
But on all of these four examples, the user has to opt-out to search for the typed string of characters. Is it fair to say that this behavior has become a convention, and as such should be used implementing such a functionality?