As a matter of the fact, everybody knows about it. In any case experienced users know about it for sure. Hyip-twins are appearing from the one source:templates. Let's start over again. So, in the HYIP field there are few scrip producers for the HYIP and GPT, and other high yield investment projects. Even the scripts for monitoring sites. The biggest of a such producers are GoldCoders and Monetary Soft (besides HYIP scrips recently they have made a script for the payment system Regalpay) There are producing lots of the templates for their scripts. Of course it's not selling officially on the shelves of the producers, but it can be easily found in the Internet. Often there are even free-ware ones (if I'm not going wrong, the pack of the free templates is included in the price of the script).
That's why it's VERY hard for the administrator of the project to make a good looking original high yield investment program, if he has a small budget. So, this is the reason why often they are looks like the same. Very often the logo are also for free. Here is a fresh example: http://www.eximfund.com/ and http://www.grandmoneyinvestment.com/ as it says find 10 differences.
Usually such coincidences are proving only one thing: the administrator is very poor (that who has started a such project), He has used not only a cheap engine (has not developed his own) but also has not took care of the design, which is free-ware or being found somewhere on the dump. Such kind of the projects can't exist for a long time, by it's definition, so stay away from them..