From what I know, this has less to do with newer or older, but probably price and performance. I’ve got two laptops – from around the same time frame.
1. The HP $400 laptop uses an older Broadcom – that when I Googled it – didn’t mention it was dual-band. (And when it doesn’t, it should be assumed it is 2.4GHz singleband).
2. The Samsung ultrabook use an Intel Centrino Advanced-N 6235 – which when I Googled that shows it to be a dual band chip – and indeed I can see both wireless networks from the one laptop.
3. And like I mentioned earlier, the family’s Apple products seem to come with both bands.
I also have a 7 year old “brick” of a Fujitsu laptop that was built for gaming (was very pricey when I bought it). And, it, too, sees both wireless networks.