Interesting discussion but as a newbie some things aren't entirely clear.
Are some choosing wider tyres (where possible) for winter rides? Safer?
Some are hinting they think accidents and damage to their bike is more likely in winter. Any evidence of this?
Rivers in an excellent post above, gives some real costs of extra wear and tear. Surprised this didn't get more discussion. However running two bikes doesn't seem more economical than one, even if replacement parts for best bike cost more?
Any other reasons for having a second bike?
Ok, let's break down some of the points you're making:-
Tyres. Some cyclists are really obsessed by speed and achieving an absolutely minimal bike weight. Tyres are one area where there are some weight savings and arguably a very marginal aerodynamic advantage to running narrow tyres. Such cyclists often run the narrowest tyres they can tolerate the ride quality from, on their best "summer bike"
They typically won't ride their "best" bike in winter, so they will run a cheaper, slightly heavier one. No-one is as fast in winter as in summer anyway, so they will fit wider and more sturdy tyres they would not use in summer.
Accidents- More riders come to grief in the autumn and winter. Adverse weather, wet roads, mud on roads from farm machinery, slippery leaves, black ice, shorter daylight hours. Crashes are more likely so the logic is it's better to crash a cheaper bike rather than an expensive one.
Multiple bikes:- The running costs of high end bikes can be surprisingly large, because of the price of wearing parts. Some riders will tolerate this all year round, others won't or just can't afford it. The price ratio between the cheapest and most expensive chains, freewheels, cassettes etc can be a factor of ten, and if you do a lot of miles that equates to a significant amount of money over time. Road salt can make a horrible mess of alloy parts and paintwork unless you are meticulous about cleaning. it's much much easier to just knock about over winter on an old beater bike you don't care about, that's fitted with low-end, cheap to replace mechanicals.
Another couple of reasons to have two or more bikes (or two of anything else0 - it gives you a fallback if one machine is out of action, and by having more than one you can optimise them for different uses. If you run secondhand rather than new bikes, then having multiple machines for different uses can work out no more expensive than having just one bike bought new.
