Yeah they need that extra quarter of sales to try and get out ahead of Apple as much as they can. As soon as the iPhone 8 is announced preorders will be insane and lines long AF. Nothing in the Android world comes close to the excitement and build up iPhone gets. Even if Samsung had more of a physical retail presence I still don't think those stores would see the crazy lines that Apple Stores do for iPhone releases.
The Samsung S series has been a first quarter release for years, as long as I can remember. It has nothing to do with Apple, instead it is because they release the new Note in September, so it is to stagger the release of their two flagship phones. From some of the early reports, it sounds like the Note will be an incredible phone this year.
As for the lines at Apple Stores, that is a negative not a positive. The reason for the lines is that Apple releases the phone before they build up sufficient back log of devices for demand; if you don't get in line you aren't going to get the new iPhone on release day. Apple creates an artificial shortage, which causes the lines. By contrast, Samsung doesn't have those shortages, they manufacture enough devices that they can meet the demand for their phones.
Don't get me wrong, I'm not a Samsung fan. I was never a fan of TouchWiz, though it does look better this year. I also like timely updates, something Samsung has had issues with.