The calls don't go over the end user's internet connection. They can be initiated on the web or through an app, but the actual call uses landlines and cell phones on the ends. Unless you call a voip user.
The texting is free. You can choose to have the text messages forwarded to a mobile phone, for which you may be billed by your carrier. Texting is not free on Skype.
There are all kinds of rules and filters you can place on incoming calls. Voice mails can be transcribed and delivered as email. All free.
When someone calls your GV number you can have it ring multiple phones or go straight to voice mail. You can set schedules of what phones should ring. You can have custom greetings for different contacts.
USA calls are free. International are 2 cents a minute for calling landlines in many countries.
It's a completely different beast than Skype. And it highlights that the major US carriers have been sitting on their hands while voip providers, Skype, and now Google provide far more compelling features than they have.
As I see this now, GV combines aspects of Skype (can be used for VoIP from computer to computer, your comment about VoIP users) with that of a calling card (you call a local number) and call forwarding and routing. Most telephone companies offer forwarding and routing to multiple phones already but it is generally (a) expensive and (b) the user interface is not that great.
Apart from the general cost savings of VoIP/Calling card type international routing, Google Voice seems to add value to the Skype model by connecting it better to traditional phones.