Re: Official fix or temporary workaround? Will WordPress eventually resolve this issue for those themes? It's bothersome to do it for each single cell.
I'm sorry I don't know. I just use what works. You will have to contact Staff for an ans as we Volunteers have no idea what they plan to do or not do. You can contact them when they reactivate the support link at 12PM UTC on Monday 27th June. http://en.support.wordpress.com/contact/
Re: It's only after I added the caption, the page wraps the image + the caption with a thin border line. Top, left and bottom borders are there, except the right side.
I could be wrong but that sounds like caption bug to me I suggest you report it.
Re: how come there is no "insert table" in the tool bar and we're forced to hand-code such a common element in HTML view?
There is no insert table, change fonts, change backgrounds etc. in the editor because WordPress.com does not choose to use equip the editor with some functions that moxiecode who provide the Tiny MCE offer. We get the basic editor.
P.S. If we use windowslivewriter we can create tables in it and post to our blogs from it. We can also use table generators online and copy paste.