Yes, but for the date and time indicator it is necessary to have text. You can't hope to convey the time in an icon that small.
In that case, text becomes necessary to convey in the information accurately. Introducing it in other places will add clutter to the setup and start a possible branch of applications that decide they want text in their indicator and possibly invite abuse.
I too hope that the weather indicator applet would have the temp. It would seem a bit contradictory to say an indicator (like weather) can't have numbers when Maverick introduces the Time and Date applet