If one wants to purchase a Raspberry Pi, there are a number of different manufacturers from whom to buy.
These include element14 and RS Electronics.
Are there any significant differences between Pi's made by these manufacturers?
They've used different colored PCB's (light vs. dark green) in the past, and that orange piece of tape -- actually, the whole HDMI connector its on -- is another. Note that Farnell and RS are not really the ultimate manufacturers either. As far as I know, they don't even do something involving assembly. It is all contracted out under their management.
The B I have with a slightly different styled HDMI connector is made in China, and I think I got that directly through Farnell/Element 14; my other made in the UK B I think I got through Adafruit but it came in an RS box. I'm not positive about that though.
However, Farnell and RS are in themselves just partners with the Foundation and distributors of the Pi. I believe there are, or have been, other such direct distributor partners that are more localized -- e.g., there was a red Pi B made for distribution in China by one such partner.
But today the Pis themselves are "mostly" (sometimes this is stated as "only", but then there turns out to exceptions) made in a Sony plant in Wales.
I believe there do turn out to be occasional minor differences (such as the HDMI jack) but this probably span time and space, and they will not simply be between Farnell and RS, although I think it's the latter that tends to be more involved with "not actually that plant in Wales".
Are there any significant differences
Not unless you count PCB color and some other cosmetic things. E.g., that the HDMI jacks are styled differently implies they have a different origins (although even that is not necessarily true) but they would still spec the same.