Astley - I think the consensus seems to be that the party child would not care or notice, that 99% of the party child's parents would not care at all, but the invitee would perhaps feel very conspicuous about not bringing a present (if they were unable to), which is a horrid shame.
This is not meant to sound boasty AT ALL, but I had quite a privileged upbringing - ponies and barding school etc. Not that I can afford same for mine, but hey ho. Anyhow, I was great pals with a boy from the village, who was really not at all well off. Not that it mattered to us. It was my 6th birthday, and he came to my party, and bought me The Best Present Ever. It was his bouncy ball, which was much bouncier than my bouncy ball. And he gave it to me! I was made up. And I've always remembered. I knew that he lad less money than me, but did not care. I knew that he did not buy the ball for me but did not care.
Years later, at pal's wedding, I told that story to the people at the table, when we were saying how we knew the Bride and Groom. I may have cried buckets a bit: it was honestly a great present as this was a prized possession to give me, and he's been a lifelong friend. And I was quite well refreshed. Then he said that he was so hard up that he could not afford any other present, that he had to come to party in his school uniform (I did not notice/recall that), and that he did not normally go to parties as he just could not afford it. At that point, almost everyone else cried, incl. all his tough squaddie mates. Honestly, the nice kids, the ones you'd want as friends - they wont mind.