I agree with Fizzatron, maintaining an old codebase is a bit like owning a 1920's Jugend style house. There isn't and won't be a day when there won't be "bugs", and in fact, the reason behind the longevity of some old buildings is that some bugs just have to be allowed to exist, so that, for example, the ventilation of the house doesn't go astray.
So "no bugs" is a completely unrealistic dream state for any program running on code that is one year older.
It is also pointless to compare a 10-year-old codebase, which has been worked on by 100 pairs of hands, with a 1-year-old codebase, which has been worked on by 5-10 pairs of hands. It's true that modern tools speed things up, but the rubber doesn't meet the road until both the object of comparison and the "comparee" are roughly the same age and magnitude.
And which one do you think is still standing after 100 years - the Jugend house built in 1920, or the end of a townhouse built in 2010.