"Táim ag siúl go dtí an siopa."
Translation:I am walking to the shop.
I think it depends on who you're talking to. I talked to some people in Munster this past summer who pronounced the g in "ag" before consonants. Personally, I prefer to pronounce it, myself.
This is one of the most basic phrases that we learn around the age of five or six and usually the /g/ is pronounced, probably because the Caighdeán is heavily based on the Munster dialect.
If you're pointing to the recordings as examples of when people do, you should be aware that there is a difference between when people speak naturally and when people are reading words off a list. It's true in any language. When reading, you're much closer to the written pronunciation, even if you don't normally say it.
Then it's either because
a) They weren't native speakers b) They've been highly influenced by "school Irish".
See here, where you can tell it's not pronounced before a consonant with the VN. And it hasn't been for a while, since Scottish Gaelic also lacks this distinction. It's also mentioned on Gramadach na Gaeilge that /g/ only appears before a vowel.