Are speakers Analog or Digital

Speakers by their physical nature are inherently analog. They are a physical device affecting physical space. 

Then why are some speakers sold as "digital ready"?

Because, marketing. Speakers work when current, a small amount, is sent through the speaker wire to the electric current flows through the coil, it becomes a temporary electromagnet. The permanent magnet on the speaker is attracted and repelled which moves the speaker cone, which moves the air to create sound.  

Are some speakers better at working with digital sources than others? The short answer is no because the source has nothing to do it the speakers function. 

Does a digital source have an affect on the sound?

Yes, what will have an affect on the sound of a digital source is the type of DAC (Digital Audio Converter) that is in your amplifier.