The "winter appeal" bit is essentially sense-free advertising drivel, probably inspired more by the suit's color and by a desire to sell it now, in December, than by anything else. There is nothing about S140's wool (nor about a dark blue suit) which limits it to winter.
This having been said, since you mention only needing one suit, and wearing it to weddings, funerals, and similar occasions, it sounds like you're shopping for a suit which you (1) don't intend to wear much; and (2) out of which you hope to get a fair number of years of service.
The first of these considerations actually works to S140's wool's benefit, since all things being equal an S140's or S150's wool will tend to be less durable than, say, an S110 wool. Exceptions exist, of course, but in general a good argument could be made for that being true. (The higher S-number may look or feel nicer than the lower S-number wool, although here too, exceptions do exist.)
If you'd planned on wearing this suit for work, an average of twice per week, the durability of the wool would be a key issue. But given your intended usage, I'd submit that it's of relatively little importance, and S140 is a good choice. Care for the suit properly, and excessive wear issues are unlikely to be much of a problem.
It's the second of the aforementioned considerations which I think matters quite a bit - the one about you presumably wanting to get a number of years of use from the suit. The suit in question is of a very fashionable, modern style. While certainly not out on the fringes of fashion, neither is it what I'd call an extremely conservatively styled suit.
And as a general thing, the more "in fashion" a style, the shorter its time in the sun. Which suggests that in this case, in a few years, the suit may still be in good shape, but its overall style - length, closeness of fit, lapel width, etc. - may leave it looking sadly dated.
If this is of any importance to you, you may wish to reconsider this suit.
Again, I am NOT suggesting that the suit is ridiculously modern and a one fashion season wonder. Just that it's not of near timeless styling, either.
But to repeat, the advertising hype may be safely ignored. The suit may be worn in summer without a second thought. It's not like it's a heavy flannel or tweed.