I experimented with this using a Linux server and a serial port. I used a MySQL database to store the data, and the server and the serial port used the database to communicate with each other. You can do it, but it isn't a simple deal.
Can I pull/request those strings via USB(or serial?) of my arduino?
maybe http get over usb?
I'm not aware of a general solution to your problem but it's quite easy to solve in a specific setup. Just use an application on the PC that waits for a command on the serial interface, calls the web page and returns the data to the Arduino. You have a bunch of choices to do that, on a Windows PC Processing is probably the easiest to deploy.