The main differences really boils down to the connotations of the words themselves. Speech is defined by Merriam-Webster as "something that is spoken,a usually public discourse."A speech is a type of oral recitation, whether from memory or notes. It is a way to communicate ideas auditorily to an audience, with a specific purpose in mind.
Presentation, on the other hand, is usually refered to as a more interactive experience. Salesmen present their sales pitch, showing the item being sold, demonstrating its good qualities, and letting the consumer ask questions. Presentations are about giving the information in a way that appeals to the audience, rather than necessarily speaking the information.