There are many things a dedicated per/pro cannot do. What a good htpc offers, simply blows away anything comparable.
1 year from now, you'll wonder why anybody would do anything but a well executed htpc.... They're that good. Here's some things I like about my setup:
It's simple. I use jriver and it took me Just a few mins to show my 60yr old mother in law how to use it. Her response "wow, this is easy!"
My entire media library is on one device.
I can browse, launch, change volume, all on my iPad or web browser.
I can stream all my content to any mobile device that I choose, converting video formats on the fly.
The sound quality blows away anything ive ever heard (separates and receivers)
The video quality is simply stunning.
It's still a fully functioning computer... And I can use it as such whenever I want.
It's infinitely upgrade able.
It's very inexpensive for what you get.