Here is a very amusing, if not helpful link:
http://www.fodors.com/community/europe/attire-for-men-in-nice-restaurants.cfm

Your husband will be fine with a collared sport shirt and khakis just about anywhere. Your go-to outfit is also perfect. Now, if you feel you haven't brought something stunning enough to dress it up, I'm sure you can find a great souvenir accessory...

There are so many tourists in those places from all over the world, in a wide variety of attire. I'd just bring something simple I could dress up with a scarf and a comfortable pair of non-athletic shoes. We were just in Venice, Siena, Rome. Even the dressiest people weren't that dressed up. Well, a few in Rome...but those were the Italians. Black pants, nice top are perfect. If you want dressy heels, fine, but pick something comfortable. No jacket for your husband.

Jamikins, I missed that thread. Hilarious!

One of my favorite and also one of the best dining experiences on Lake Como is the Veranda Restaurant at Villa d'Este. For men, a jacket and tie is required in the evening.

"but is a dress necessary"

A woman in Italy, guest or native, will always get better treatment if she looks sexy and feminine. I always wear a simple yet fabulous dress if I intend to dine in a finer restaurant. The perks definitely outweigh the cons.

I always take a couple of dresses and nice pants outfits (usually silk) for going out to dinner and the beau always has a blazer or jacket. We feel more comfortable dressed this way at many of the places we dine. that said - most do not have specific dress codes - although I believe you will be more well treated if you make it apparent you respect the restaurant and the staff.

That doesn't mean you need to dress that way for cafes, trattorias, tavolda caldas, etc. for those any decent sightseeing garb is fine. (But I still don;t like to see strange men's fat hairy legs while I'm eating - I don;t get why they can;t wear big boy pants.)

<I always take a couple of dresses and nice pants outfits for going out to dinner and the beau always has a blazer or jacket.>

We do the same. Choose fabrics carefully and packing will still be simple.

My husband does not wear khaki's but packs nice slacks in fabrics that travel well, like wool gabardine.

The first year we went to Italy my husband brought a jacket. It was June and Africa hot. No restaurant we ate in had any men in jackets. He never took it out of the suitcase. He wears khakis and a nice polo or long sleeved shirt and I wear a casual dress with flat strappy sandals.