Yes, those numbers on your DM screen are accurate according to the Rules Compendium, as Brian pointed out in his answer, and yes they're supposed to provide roughly that chance of success. I'd like to tell you why and what to do about it.
Due to their heroic and epic nature, characters in 4th Edition are supposed to be able to automatically beat easy and moderate skill checks, even on a roll of 1, if they've spent effort and resources on it. They've trained so much and are so good at it, that there's just no chance of ever failing.
What this means is that instead of rolling whenever they attempt the relevant skill, you're supposed to just narrate how awesomely they accomplish it.
This is completely fine, if that's what you want in your game. However, if you think it's a bit boring and want to roll more dice, or feel like it's just too easy and that there should be some chance of failure, here are two house rules you could introduce. I'm not sure how common they both are, but I've used them both with success.
Fumble on a 1. With this rule, a 1 always results in a failure, even if the roll actually beats the DC. This risk can provide more interesting gameplay and excitement, however, it could also be frustrating for a player who went all out to maximize a certain skill. It could also be argued that such a character would find the skill trivial to use when the task is easy or moderate, and that an inherit 5% chance of failure would be unacceptable.
Introduce a Very Hard DC. I made a new DC chart with two additional columns: Very Easy and Very Hard. While I've never really used the Very Easy column past the heroic tier, because the tasks where it would've been relevant were too trivial to roll ever for, I still occasionally (maybe once a session) use the Very Hard column when the players attempt something that's a huge challenge. It's 3-4 points higher than the Hard column, so the players still have about a 20-25% chance of success, before using any powers or consumables that give bonuses.
If you're starting a campaign, you should of course talk to the players and DM to find out what they want, before you use any of these rules.