David Hare-Scott wrote:

http://www.ph-meter.info

Interesting site. How is it relevant to the original question?

Partially only, but it is a good introduction to pH measurements. IMHO
it is better to know a little bit too much, then not enough

Are there
any glass electrode portable systems suitable for use in the garden?

Google for pHC2051 made by Radiometer - that's the electrode. pH meter
is a separate thing, there are battery field units available from many
manufacturers.

For garden or agricultural purposes why would you need
accuracy down to decimal points of a pH unit?

One decimal point my be important, as soil pH changes in rather small
range - and the difference between 6.5 and 7.5 is rather important,
while every soil in this range will be measured as just 7 (perfectly
neutral) without any decimal digits. But IMHO you don't need the pH
meter in a garden, for most cases pH stripes will be enough. Especially
if you will use not universal ones (0-14) but some for smaller range.
See examples at http://www.indigo.com/science-supplies/ph-paper.html -
there are papers for range 5-9, while these described on the page are
targeted at body fluids, I am more then sure that you will find similar
ones for soil measurements.