Points after sentences on Twitter homepage

I just visited Twitter's homepage. And it's actually a really nice converting homepage. Almost felt the urge to register.

But I was wondering a thing. The homepage has a few short sentences, after some sentences a point is placed, after some not.

I'm pretty sure this has something to do with user-interface/the way people read websites. In Dutch there is no gramatically reason to do this.

My question: How did the user-interface designers decided after what sentence to place a point, and after which not? Is there a rule for this?

This is what I came up with after thinking myself:

1. It's because some separated sentences actually belong together linguistic. This is wrong in my opinion, because each sentence start with a capital letter indication a new sentence. So actually after each sentence a point should be placed, which is not the case here.

2. It's so people will read two sentences as one e.g in the right part they say: "See what's happening in the world right now" -> "Join Twitter today". Maybe they didn't placed a point because now people read it as one sentence, and are someone more coinvinced that by joining today the are staying updated by what's happening in the world?

Also notice, that different languages have different point-placements. The Dutch version of the homepage for example doesn't have a point at the end of the first sentence, where as the english version has.

TL;DR: How did the Twitter user-interface designers decided after what sentence to place a point, and after which not? Is there a rule for this?