My observation is that the most common reason given is that Silver or Gold was the 2nd gen game they got originally.
Maybe...... but a lot of people like Soul Silver better because they like Lugia more than Ho-oh (which includes me!). That's probably why they bought Silver in the first place.
Anyways, I bought both last time, and I'm buying both this time! The first time was because I knew there would be version exlcusives. However, this time, between D/P/Pt and the GBA games, you can all the pokemon without needing both HG and SS. The reason I'm getting both this time is because 1.)I like how trading Groudon/Kyogre to the other game makes Rayquaza show up (so cool!) 2.)Together, I'll no longer need to mess with GBA games so much and 3.)Having two means I can restart one as much as I want and still have a "main file".
And besides, I've always bought both, anyway. I'd feel like I'm missing a piece of the puzzle if I didn't buy both!
I still have all the main games, BTW. It's getting harder and harder to keep up with them, though, because they get stored away for years and I forget where they are! :P I finally decided to keep the GBC games in my "Fire Red" box, and the GBA ones are in a pouch made for GBA games.
Ironically, the only one I ever lost was Silver <-----My favorite game =/ (but I bought a replacement, so it's okay)