I agree it is hard to draw a line between the two, but there are some decisions that occur outside of the technology inolved that I would consider product development. Twitter increasing the character limit to 280 is a prime example. There is no technological reason why that should or needed to happen. It was motivated purely by the product. Although you could argue the initial 140 limit is closer to the tech side.

I also think that many people, especially in the tech industry, don't understand the scope of functions included in "sales and marketing". It isn't just sales people calling up customers trying to sell enough to reach their quota. It is nearly everything involved in revenue generation of a company.