earphone compatibility?

I've had a few iPhones now so I've worked up a small collection of the earphones in the process. If I plug my original iPhone 2GS earphones into my 2007 macbook, I am able to use it for both sound and mic, which is perfect for when I use skype. For some reason though, the more recent earphones with my 4G will only give me sound and no mic. I cannot understand the difference? I thought they were both TRRS connections, they certainly look the same anyway

Here's a picture of both, the 4G on the left and the 2G on the right. Sorry its not great quality, if a better one would help I can sort it out

Thanks

Is it because there is a microphone already on your macbook?