I have mentioned in an earlier post that geographically I have no knowledge of Scotland at all. Crathie and Braemar has always been stated as being in Aberdeenshire when I have searched. When your post mentions Deeside, which I havn't come across in my research, I didn't make the connection. I now know in fact that there is a connection.
 Yes.
Braemar is a small town in the parish of Crathie, and the River Dee flows past Braemar and Crathie and continues past Ballater, Aboyne and Peterculter (among others) before entering the North Sea at Aberdeen. Deeside is a name applied to the part of Aberdeenshire lying on both sides of the River Dee.
The more I think of Robert being in Australia the more I think it unlikely. Even though the general online search suggests it may be true. Without paper and document evidence it is impossible to be sure.
The official Victoria deaths index lists a death of Robert Clark, aged 92, parents James Clark and Janet Morris, in Echuca in 1902. So it looks as if this is indeed your Robert Clark.
As for his DoB, his baptism was in 1810, so the age on his death certificate is spot on. I wouldn't worry too much about his age in the census being out by a year or two. This is quite common, and Morice/Morris sound the same.
There's also an index listing of the death of Ann Clark, aged 72, parents Andrew Philip and Margaret or Mary Malcolm, in Echuca in 1892. There's no matching baptism in the surviving records, but Andrew Philp and Margaret malcolm did have two other children
Mary, baptised 5 November 1820 in Dundee
James, baptised 2 June 1822 in Mains and Strathmartine - which is the parish where Ann Philp or Clark was born, according to the census.
I see that a Margaret Philip or Malcolm, aged 82, mother's maiden surname Robb, died in Monifieth in 1876 aged 82. Monifieth is the next parish east from Dundee, and Mains and Strathamartine is the next parish north-west of Dundee. It is where Robert Clark and Ann Philip married in 1840. It might be worth a look at that certificate. 
So it does look as if Robert and Ann emigrated to Australia. The original 1871 census does say quite clearly 'widow' but perhaps the enumerator got it wrong, or perhaps Ann herself was being economical with the truth.
You could get copies of the death certificates to provide the documentary evidence.