Here is what a Level 30 character could have, if optimized to hit.
- +15 Levels
- +10 prime stat of 30 (assumes an extra +2 to the prime stat from Epic Destiny)
- +3 an expertise feat
- +6 a +6 weapon
- +3 weapon proficiency bonus
That's +37 without anything special added. You'll need an 11+ to hit Demogorgon, right at 50/50. Attacks against other defenses vary considerably, but figure 2 less as a rule of thumb.
A character not as optimized to hit will be probably 2 less:
- Not having a stat boost due to an Epic Destiny
- Using a weapon with only a +2 proficiency bonus
There are several ways for a character to improve his or her chance to hit
- Fighter weapon talent
- Rogues weapon talent
- Kensei Focus
- accurate implements
A character devoted to hitting should get an extra +1 from somewhere. Throw in
Combat Advantage and you are swinging at +40. That should be enough to have a reasonable chance to hit most anything.