The difference illustrates a strategic divide between the two tech rivals.
Apple is betting that customers will not use voice commands without an experience similar to speaking with a human, and so it is limiting what Siri can do in order to make sure it works well.
Amazon puts no such restrictions on Alexa, wagering that the voice assistant with the most "skills," its term for apps on its Echo assistant devices, will gain a loyal following, even if it sometimes makes mistakes and takes more effort to use.
The clash of approaches is coming to a head as virtual assistants that respond to voice commands become a priority for the leading tech companies, which want to find new ways of engaging customers and make more money from shopping and online services.
PATH TO THE MONEY
Now, an iPhone user can say, "Hey Siri, I'd like a ride to the airport" or "Hey Siri, order me a car," and Siri will open the Uber or Lyft ride service app and start booking a trip.
Apart from some basic home and music functions, Alexa needs more specific directions, using a limited set of commands such as "ask" or "tell."
For example, "Alexa, ask Uber for a ride," will start the process of summoning a car, but "Alexa, order me an Uber" will not, because Alexa does not make the connection that it should open the Uber "skill."
After some setup, Alexa can order a pizza from Domino's, while Siri cannot get a pizza because food delivery is not - so far - one of the categories of apps that Apple has opened up to Siri.
"In typical Apple fashion, they've allowed for only a few use cases, but they do them very well," said Charles Jolley, chief executive of Ozlo, maker of an intelligent assistant app.
Apple spokeswoman Trudy Muller said the company does not comment on its plans for developers.
Amazon said in a statement: "Our goal is to make speaking with Alexa as natural and easy as possible, so we're looking at ways to improve this over time."