The same could be said of the differences between the original Castillian Spanish and the Latin Spanish in South America or the differences between American English and the original English (with the correct spellings).
English itself is an everchanging conglomeration of various languages. Mainly it comprises of mainly 70% Saxon, 10% Gaelic, 10% French (thanks to the Viking invasion from Normandy via William the Conquerer in 1066) and a 10% mixture of other languages including Nordic, Hindi, Chinese,Spanish, Italian and Latin.
Unlike other languages, English tend to readily adopt more useful words from other cultures and languages, including grammar occasionally. It does make it more difficult to learn because of the numerous and strange grammar exceptions to the rules.
It lacks the handicap of pointless "male" and "female" nouns and verbs that plague some other languages due to English's ancient Gaelic foundations.
English is the only language that uses the very useful concept nouns of "It", "That" and "Thing". Try completing a day without using any of these words to realise just how useful they really are in preventing longwindedness in simple conversations....
American "Wilsonised" English with its simplified "bad" spellings does address some of learning barriers but also annoys the hell out of us true English speakers.
The two explainations / excuses I've heard are that (A) it was revised in order to make English easier to teach to children and non English speaking immigrants or (B) the US didn't want any written or printed words that looked French hence the dropping of the letter "U" and the reversing of all ""RE" ended words to "ER" or (C) it was to annoy the British.