It was SMTV that was hugely popular and was the ratings draw, not CD:UK. CD:UK was painfully bad over its final 18 months (and had been on the decline since Ant & Dec left). The Chart Show was as popular as it had ever been when it was axed- more than can be said for CD:UK. I doubt it would have been anything more than moderatly popular if it was on its own, without SM:TV. And, anyway, SM:TV wasn't a runaway success, it was on the verge of being axed for most of the first year.
The thing about the announcer talking over the last episode- I presume that was only in his region, both copies of the last episode I have (all but the last 5 minutes of the one I taped accidently got wiped, someone else sent me a copy)- one from Yorkshire, one from Central- have no announcer over the end.