At the end of the say size does indeed matter with image sensors
because the size of an individual photodiode is roughly proportional
to the sensor dimensions (assuming the same megapixels). There's a very
simple rule: the bigger the size of the photodiodes the less image
noise will occur. Just think of how many photons can be collected by a
when less photons are collected the data gets less precise - the
variation between neighbouring pixels gets higher = more noise.
The following chart provides an overview of the current pixel
pitches in today's (pseudo-)DSLRs.
It should be quite obvious why cameras such as the Minolta A1 or the
produce much higher sensor noise compared to the "real" DSLR family.