Capitalization for sentences divided into a few lines

Hello,

I am very well aware that grammar, unlike for example maths, does not have to make sense, it just is. However, sometimes it does and I would like to delve into one case to find out.
In English, there is a rule saying that every sentence should begin with a capital letter. So far, so good, but what about the sentences that start on one line, then stop and continue on another line? Should this second line also start with a capital letter? Based on the rule above it shouldn't, because this is still the same sentence, but somehow people begin it with a capital letter.

Example 1:

Dear Jake, how are you today?

Example 2:

Dear Jake,

How are you today?

According to this article http://en.allexperts.com/q/General-Writing-Grammar-680/2008/5/capitalization-letter-salutation.htm they are both correct, but it does not make sense. Both are the same sentences - just differently presented.

My question is: Why is the second one correct (How instead of how)?
I haven't heard about the rule saying that we should begin all/some/chosen lines with a capital letter.