For those of you who may not be up on the jargon: A mashup is a Web Application that combines data from more than one source into a single integrated tool (Wikipedia). A good example is the integration of Google maps into a Real-estate Website. Two distinct applications mashedup to create an enhanced solution to your property hunting needs.
The paradigm shift of the players like Google, Amazon and the likes of Salesforce.com are to create platforms with which you can Mashup. The game being that the more applications that incorporate these larger players' technologies the more imbedded the player and the more reliant we are on them going forward. The best example of this kind of reliance of course is the Microsoft operating system with which so many computers are shipped each day. Companies in this space must create this reliance in order to survive the long term.
The smaller technology companies are given a chance to make the most of these platforms for development by being allowed to bolt their own applications and data into the platform to create a new product as such. I'll give another example just to make it a little clearer. In a local tourism website you could have an imbedded map which when clicked on reveals Flickr photo's of sites to go and see, where you click your mouse. This will of course help you plan a trip more effectively and let you have more fun planning it.