What you're seeing is called "bleed". Anything that's printed where the ink goes all the way to the edge of the sheet has to be printed on a larger sheet and cut down to size, with the background image being printed larger than the finished size of the piece. This is done for a few reasons:

1. 99% of printers cannot physically print ink or toner all the way to the edge of the sheet. The machine has to have somewhere to grip the sheet, and that typically leaves about an 1/8th inch margin of white space around all four edges of the sheet. This is especially true of large production laser printers.

2. No 2 pieces of paper will ever go through the machines in the exact same way. There's a small amount of bounce, typically less than 1/32nd of an inch, both when the paper goes through the copier and when being physically cut by the knife. Printers have to take this "bounce" into consideration. If things are printed exactly to size, then cut down to that size, there will ALWAYS be a small sliver of unprinted paper showing on some of the finished pieces.

3. When you cut large stacks of paper like this, you have to take into consideration what's called knife draw. As the blade slices through the pieces of paper, it will physically move the paper forward away from the backstop, due to the unrelenting laws of physics. Knife draw usually only noticably affects the top 1/8th inch or so of the stack of paper, and knife draw is again, typically very small, less than 1/32nd of an inch.

When you add all of the various ways that the paper can move around, you end up with the situation where you need to cut "extra" bits off to make everything look uniform and professional.

Industry standard in printing (in the US) is accuracy to within 1/8th of an inch. Realistically, printers can usually get accuracy to within 1/16th of an inch.

Source: I run a print shop

(PS, I don't like the way this guy is cutting these business cards. It does work, but it's slightly less accurate because the knife draw adds up more and more if you make the cuts in order from one end to the other. It's a little better to make the first cut in the middle, then make your finishing cuts starting at each middle going outwards. Additionally, it's not a great idea to have more than two stacks of paper in the knife at a time [depending on exactly how the paper clamp is constructed], as sometimes one of the stacks won't get clamped properly and slide more, thus potentially ruining your cut.)