Pretty much. And if they could replace just the glass, it's a lot more work. (Replacing less is more work? Yes - they'd have to heat the glass just to the point that the glue bonding it to the layer beneath it softens just enough - and all over the entire glass at once - and the temperature range between that and damaging the screen is a few degrees, so it takes a very experienced tech and a lot of time - and that means a lot of money.) Besides, the body holds the glass in and it's probably damaged enough that they won't guarantee the job unless they replace it. If they replace the body, the back panel has to be replaced.
An expensive, very protective case is a lot cheaper. An Otterbox Defender for the S8+ is only $70 - about £55. A lot less than broken glass, (If you saw my Note 3 fly into a wall glass-first, with a lot of speed, you'd understand why I'm recommending it. Not a mark, not a scratch - to the phone, the case, the wall, nothing. That was 4 years ago - I'm selling the phone now. It still looks brand new. And I've dropped it a few other times. At 76, you're not as sure-fingered as you were when you were younger. Still not a mark on it.)