If Nigger's gravestone has been removed for 'Politically Correct' reasons, then this is a minor example of the ever increasing airbrushing and sanitizing of history by the PC brigade and is to say the least niggardly.*
Whilst I consider the usage of Nigger as extremely offensive when used either to describe, or worse denigrate a person today, but it is an unchangeable fact that it was in general use both historically and up until relatively recent times.
From recently hearing a conversation in West London accents where the word was used extensively, it appears that providing you are of West Indian descent, then using the term is perfectly acceptable even in the 21st Century, but now it depends on who is using it!
*Niggardly - Mean, Ungenerous, first used 12th centrury and predates words such as Negro by a least a century and a half. therefore should not cause offence (except apparently in an office in New York, but that is maybe an urban myth).