I have a Sony DVD recorder RDR-GX300 which can use both DVD-RW and DVD+RW. But in the manual it only says it will record 4:3 format on the DVD+RW and not 16:9. But the DVD-RW it will record 16:9.
Does this mean that you cannot record 16:9 format onto any DVD+RW?

It has been noted before on this form.
Do a search on this forum 'dvd+rw'
On my gxd310 a 16:9 programme is recorded as 4:3 (not in the correct aspect). On playback the tv detects 4:3, manually switching the tv to 16:9 and the aspect ratio is correct.

Its a strange one from Sony, I have the HXD710 and it is the same. no 16:9 on any +R/+RW/+R DL only 4:3 letterboxing of the 16:9 recording.

From past comments on this forum people have contacted Sony about this and it seems they aren't bothered about fixing the problem.
Strange really as Sony were one of the high profile proponents of the + format.

I was surprised when I went from a Philips DVD recorder to my current HX510 to find +R 16:9 recordings were squashed to 4:3.

I actually think it is down to the +R system itself and not the Sony. When I played recordings made with the Philips unit on my new sony recorder or my sony player they too were squashed to 4:3.

Seeing this I assumed all +R machines did this (backed up by some further reading) but other machines handled it better than others.