This happenes because of currency exchange rates:
When apps are published in the Google Play market, the developer can set the base price of his/her country, and optionally the ability to set prices in other currencies. If the developer didn't fix the price in other currencies, then the Google Play market will do the conversion using the currency exchange rates (weekly? have no idea).
When the exchange rates are modified, the app price gets modified by few cents, and this triggers the Updated action for this service.
Currently I do not plan to add other methods of notifications for this service, but this can already be achieved by using ifttt service.
An example (mini tutorial) on how to receive notifications by email is on my blog: Get update notifications by email.
Just copy the feed URL (such as http://www.appfeed.net/feed.php?t=f5289b83f059af177f41ff172220ae8b and paste it in you feed reader, or into Google Reader, and it is done.
Currently the service is free, but hosting and bandwidth costs money, so currently users who sign up are limited to add up to 25 apps, if a user requires more apps, a donation will convert the account to a "Donate Account" which increases the app limit to 100 apps, but all depends on the donation ammount.