I'd say there really isn't much difference in usage between American English and British English. In both dialects, it can be used to mean "it's alright", and dismissively to mean something like "shut up, I'm annoyed". A lot of it depends on tone of voice.
American English is a living language spoken and written by millions of people in the year 2014, that continues to evolve.
British English is a living language spoken and written by millions of people in the year 2014, that continues to evolve.
Both have features and vocabulary that the other once had and since lost (or at least which is now less commonly found in it).
Both have innovations that the other has not adopted as eagerly.
Describing either as archaic or modern compared to the other is meaningless (now Yola for example, is a form of English that is genuinely not modern).
It could certainly make sense to describe one as more innovative in a particular regard, but in actually examining the two we find that the two seem to keep apace for the most part.
There's perhaps more spellings that differ from how they were in 1801, due to Webster's reforms being more heavily adopted in the US than the UK, however:
- Many of these were a matter of him settling on one of two or more forms found in both the US and the UK, so in these cases neither is necessarily the more modern.
- Many were adopted in the UK too.
- Many were not adopted in the US.
- There were spelling innovations in Britain such as beginning to favour -isation over -ization.
We find verbs changing forms more strongly in one than the other, but it will sometimes be British English that is the innovator, sometimes American.
We find many neologisms in American English, but also some relics like teamster being used long after any teamster dealt with horses.
A great many differences relate to concepts or inventions that are themselves relatively recent, and hence the term for either is equally recent in both.
A lot of terms have come into one of these countries from its immigrant populations and its imperial adventures, but different terms have come into the other from its different immigrant populations and different imperial adventures; while US soldiers may have become "gung ho" later than than for UK soldiers missed "blighty", there isn't really much justification calling one more of an innovation than the other.
Really, while one could spend time producing a thorough score card and argue one way or the other on the basis of it, in any meaningful sense they're both about equally modern.
Best Answer
I think most would agree that any modern English variant, from anywhere in the world, is very, very different from Old English. However, I would say American English is more similar to Old English in some respects than modern British English is.
The most striking way, in my mind, is the stronger retention of the 'r' sound. I have heard (from a professor speaking on the radio; I don't have a citation) that American English generally sounds more like Old English than British English does. (In my oversimplified way of thinking, spelling has changed slower than pronunciation, and American pronunciation generally seems to stick closer to a "naive" interpretation of the letters than British.)
In other ways, of course British English is more like Old English than American is.
While not credentialed, here is a nice discussion on the topic: Which accent is more similar to that of the old English?