Retina display vs old style display, why not use @ 2x files for both?

Question

I am currently developing an application for phones with 3.0 and iPhone 4. My designer made a high resolution and a low resolution version of the design. Our application is now 6 MB, and I personally think that it is a lot, so I was wondering: why not only use high-resolution resources for all devices? What are the disadvantages of this technique?

Thanks in advance Bart

Answer 1

: . , . , iPhone 4, .

Answer 2

. . , PNG ( AI PSD). , PNG , (. ).