Well, that's one way to look at it.
The 7.1 receivers usually have their own proprietary 7.1 format, because as you mentioned there is very little media out there if any that uses it. HK's is Logic 7, I believe, someone correct me if I am wrong. You can use this on any signal coming into the receiver and the receiver will break it down into 7 channels. I have heard good things about it from people who use it and say they won't go back to 5.1. If it receives a 5.1 signal it will create the back 2 channels, if it is a 6.1 it will split the back channel signal into two. However, if you are looking to save money, the thing to do might be to just get 5.1 right now, then later down the road when you have a little more money available buy the final pair of speakers.
If anyone else has anything to add or correct me on feel free.
As for speakers, Infinity and Klipsch are both made by HK as well, so they should go well with the receiver. Klipsch seems to be more hit or miss as far as if people like them. A lot of people feel that Bose charges too much money for their performance and are trying to make extra money off of the name. They may not be the best speakers if you are looking for bang for your buck.
I hope to be getting a 635 later this year, and at that time I will probably look at Infinity speakers. But in the end all that matters is what you like, so if you're able to listen to the various speakers then get what sounds the best to you for the money. Sorry I couldn't be of more help with the speakers, I have less experience with varities of speakers than I do receivers, which isn't much.