A few more answers....
A lot of tack is sewn to either join two pieces of leather, or to increase it's durability. Stitching the leather helps to keep it from stretching, and you'll often find that tack is pretty thick because thicker=stronger.
Bronc straps are typically a good bit thicker than 'standard' tack because of the nature of it's intended use. While breaking a bronc, you most definitely don't want to have a piece of gear break and lose (what you think is) control.
Yes, you most certainly can use a sewing machine, and unless you just LIKE sore fingers, it's highly recommended. There are a lot of machines to choose from, and some are better than others. We have an entire sub-forum dedicated to the discussion of sewing machines, and there's more info there than I could retype in several years. My advice on a sewing machine is this: Buy the uppermost limit of what you can afford. Get more machine than you think you'll use, because you'll need it on the next job. One of the most popular and well reviewed types of machine is the clone(s) of the Juki 441, and variants. They'll handle a wide range of projects with ease. If you look at the Ad Banners at the top of the page, you'll see our advertisers. Just click on the links to find out more about them. A word of caution- For a good machine, EXPECT to pay upwards of $1500 dollars. Most of the "Industrial Leather Sewing Machine" you'll find on E-bay just don't have enough arse to do the job correctly. Stay away from the "head only" deals unless you're a sewing machine mechanic, or intend on becoming one. The advertisers selling machines here, have machines that are set up for power and control, and usually include a DC motor and a speed reducer. Standard 'industrial machines' use an AC motor that develops its power at high speed. They are built to run at 2-3000 stitches per minute in a factory setting. It may seem like a deal, but by the time you do the conversions, you've spent a good bit of money.
oops, looks like I got to rambling.....more info like this in the sewing machine forum.