Generally, I am impressed with the “grammar check” of Windows and find it very helpful for me and those whom I employ. However, it does not catch the comma in front of the conjunction between independent clauses making the two independent clauses a compound sentence.
Why is that? Has Bill Gates decided that this specific piece of puncutation is no longer necessary? Or is it too hard to program in? Or did his grammar wiz-kids just miss putting it in?
Using a comma for separating conjoined independent clauses is a stylistic preference that many good writers follow, but it is not a universally accepted rule. From The Blue Book of Grammar and Punctuation, www.grammarbook.com:
Microsoft probably doesn’t follow the preference because it did not appear in whatever usage manual its programmers were following.