In the redesign of Street View in Google Earth 6.0 the zoom capability found in the previous version was removed. A number of users have asked for this feature back so stay tuned to see if it appears in the next version.
Google Earth 6.2 has brought back a zoom feature in Street View using the mouse scrool-wheel to zoom in/out.
Google Maps has a zoom feature in Street View as well as other features (e.g. 3D mode) not found in Google Earth.
Google Street View is a technology featured in Google Maps and Google Earth launched in 2007.
Google Maps from the web browser and Google Earth from the desktop can view Street View. you can also view traffic.
In Google Earth v6 you drag the new orange "pegman" icon (found near the navigation controls) onto the map to enter Street View. As of Jan 2012 Google has discontinued Street View support in Google Earth 5.2 and earlier.
by google map or google earth
When Google updates it street view photos in its image database then these updates are made available to Google Maps and Google Earth.
on Google earth but you have to download it first
Here is one of Google's announcements of ending Street View support for Google Earth versions 5.x and older. "With the most recent update to Google Earth (6.2), we are also finalizing our transition to a new method of delivering Street View imagery in Google Earth. This means, that the older versions of Google Earth (anything before 6.0) will no longer be able to access Street View. We held off making this change until now, when the vast majority of Google Earth users are on 6.0 (or later)." -- Google Jan 2012. Basically, Google decided to improve the Street View interfaces which would be implemented in the current versions of Google Earth for desktop and mobile platforms rather than keep supporting the older (less efficient) method of accessing Street View.
The Street View images that are used are not necessarily taken at the same time as the images that are used in the mapping version of these online tools. Therefore one might be a couple of years older than the other.
Not yet for Google Earth. Google recently created historical imagery for Street View on Google Maps. If historical imagery is available then a clock and date will be displayed in the upper left of the map.
To compile Google Earth street view photos, Google send out vans with panoramic cameras. Because it was and is an huge task, some images are not up to date, but it is an ongoing process.
The latest (non-beta) version of Google Earth is 7.1.7.2605 released in Oct 2016. The previous stable version was 7.1.6 released in May 2016. The initial version was released in 2001. The 7.x and 6.x versions of Google Earth version include Street View, viewing Mars, Sky view, looking under water at things like the RMS Titanic, a Flight Simulator, among other useful features. Note as of Jan 2012 Street View is no longer be supported in Google Earth 5.2 or older.
You can, but it is a rather new functionality added to Google Maps / Google Earth, and at the moment, the street view is only available for major avenues and roads.