I suspect it's more the lack of really hot days in these northern climes that cause these wardrobe crises. We have little need for hot weather gear, so don't buy it. As gembo will attest, I'm wearing a linen dress shirt (and suit and tie, tie-haters) today. I think it's the fourth time I've had occasion to wear the shirt to work in the 5+ years I've owned it.
We also don't have much practice of wearing warm weather gear, so there's a high risk of getting it wrong.
The Italians seem perfectly able to carry off the suit and tie (or no tie, if you prefer) in high temperatures, but those suits will be made of a sensible lightweight linen, as opposed to the standard-issue Brit wool number.
They probably have more suits in their wardrobes than Johnny Brit as well. A stylish turn-out is perhaps higher up the cultural priority list there than here?
I don't have a problem with suits and ties. They can look very stylish. However, they don't work for everyone, and an ill-fitting suit is not a good look, and possibly a worse look than trousers and a shirt.
The problem employers have is not being able to trust their employees to dress "appropriately" for the workplace, especially as (as is all to clear from the sights you see on a sunny day) everyone has a different view of what appropriate dress looks like...