Some families really do seem to make a big deal out of 'ordinary' birthdays.
I live on a 'bog standard' cul-de-sac of a Barratt Homes estate in a predominantly working class area. So my neighbours definitely don't have film-star lifestyles! But I've overheard one guy admitting that he might have gone a bit overboard with spending £2000 on fireworks for his daughter's 5th birthday and there are several houses where birthdays (of both adults and children) are celebrated by cordoning off the end of the road and filling it with bouncy castles [note my use of the plural - one wouldn't be enough for some of these people!], barbecues [plural again!] and even a DJ with a full sound system. That means that, several times per year, we have noisy parties going on in the street outside until 2 or 3am (with kids of even pre-school age playing and screaming until midnight). The cost of each of these parties clearly runs well into four figures (even without any fireworks!).
So perhaps whatever happened in Eastenders (which I don't watch) wasn't as unbelievable as it might have seemed?