I am speaking from my own experience, and only about the commas. Also, I am speaking in the most general way – which I still find useful, though.
The main difference is that in Russian, punctuation is made according to how one's thought is built, and in English, it is made according to how one's thought is expressed. That is, in Russian the thought is divided in blocks according to the importance of its components for the completion of minimal ideas (correlations between things), and in English, such correlations are divided in blocks according to the importance of its blocks for the attention of the listener. In Russian, punctuation separates statements of correlation between things, and in English, it separates units of the reader's attention.
Thus, the comma after “in English”, like in the previous sentence, is desirable in English and forbidden in Russian. The word “in English” is absolutely a part of the correlation that is named by the verb “separates”, and thus it couldn't be separated from the verb, if the text was in Russian. All other rules work like that, too. Say, the initial phrase in a letter (“Hi John!”) does not contain just one correlation of things (the address and the greeting are not a statement of correlation, as “hi” is no verb, and therefore we have two such “statements”), but it is still the same unit of attention, so it deserves no comma in English.
I find the same reason for the fact that the English punctuation is less strict: how one's thought is composed from the constituent ideas (one could say, propositions) is a more strict matter than how one's attention is divided over it. The second question permits a lot of leeway.
For completeness of the answer: most Russians punctuate their texts the English way, anyway. That's most annoying and sometimes hinders communication, but that's how it is.