Hi JR,
Thank you for bringing this up.
The short answer to your question is "yes you can" but I'll attempt to clarify things:
simpleContact Pro was originally priced at $25 for a single-domain license, and $60 for a "developer" license that permitted you to install the application on as many of your websites as you want. I later started selling the application through the CodeCanyon marketplace, on a non-exclusive basis (I was also selling it directly here using PayPal).
CodeCanyon choose the price that they want to sell your product at. This isn't all that uncommon – Amazon do that – but it can be undesirable if they choose to sell your product for less than you'd like. They chose to sell SCP for $11 which, considering many people these days seem to think the standard rate for software is $0.99, is still pretty good for me so I decided to give it a try. They also offer an "extended" license option for products that I was able to opt in to.
Since putting it on, most sales started coming from there so I decided that it was best for me to sell it exclusively there (in order to get a better revenue split). As far as I'm concerned, the extended license is the new developer license and by purchasing that license you're welcome to install it on multiple sites.
I still believe that it's the best value way to buy the application if you're a web designer who works on many sites. It's not quite as economical compared to the single-domain license as before (at the cost of five single domain licenses), but it's a little cheaper than it used to be at $55 so hopefully that makes up for it.
Also, because of the way CodeCanyon works, single-domain and extended license holders will be able to get all updates that I release.
I hope that was helpful. If you have any other questions, fire away :)