Remote Application iPhone

The app itself is not responsible for the signal (or lack thereof). The strength of your WiFi router is the real question here. 75 yards is quite a ways when you add in walls and other obstructions. Unfortunately the iPhone doesnt have IR like real remotes, so WiFi is used to perform and imitate the functions of a remote. You could position your router closer to the location that you use the remote app, or buy a signal booster or wireless repeater (or a separate access point) to add to your network. AirPort Express is just another wireless access point that acts pretty much the same way your router does--it doesnt need an internet connection to broadcast a network. Wireless networks are a means of broadcasting internet, but they do not require internet connections. AirPort is no exception to this. If you are looking to buy some kind of wireless device like the ones I stated above, look at what type of wireless signal your router uses. All iPhones support 802.11b and 802.11g, and the iPhone 4 also supports the 2.4 GHz version of 802.11n. 802.11n is fairly new is considered to be the best signal, so look for wireless devices that are compatible with YOUR devices and have the best signal type. (In order from worst to best -- 802.11a/b/g/n)
Heres a good article that discusses how to extend your WiFi signal: http://reviews.cnet.com/1991-11334_7-6271405-9.html
Dell Dimension 5150, iPod Video 80GB, iPhone 3GS iOS4, iPhone 4 Windows XP XP Home Edition (SP3)