When they first announced the change they said top picks--so guys sure to go in the draft. The number bounced around is 10.
From the 2 drafts I attended, guys taken in the 3rd and 4th round attended with their families
Where did you see 10? From the six drafts I've attended, it was hit and miss by the time the third round rolled around. Usually if some ranking had you listed in the top two rounds, those kids would show up just in case they were a surprise 1st rounder a la Mark Visentin. An unexpected highish pick like Wayne Simmonds didn't attend and found out he'd been drafted while he was driving.
Most of the middle round guys would only show up with immediate family although I do recall Mathieu Corbeil-Theirault (4th rounder 2010) having a large contingent; Their loud celebration broke up the general silence as that round was going on.
Since I'd remember the Devils picks more vividly:
2010: Scott Wedgewood was not present in the 3rd round whereas Maxime Clermont was there when he was taken in the 6th.
2011: Blake Coleman and Reid Boucher were present when taken in the 3rd and 4th.
2015: Blake Speers was present when he was taken in the third (his family friend pinged me on HF to get the photos I took of him shaking Ron Francis' hand on his way to the Devils table since they were all SSM folks). Colton White (4th rounder) appeared to stay home while Brett Seney (6th rounder) was there.
2017: It looks like Fabian Zetterlund (3rd rounder) stayed home while Reilly Walsh, Nikita Popugaev, and Jocktain Chainey were present.
2019: All five of the 3rd/4th rounders were there.
2024: Mikhail Yegorov (2nd rounder) wasn't there but 3rd rounders Kapser Pikkarainen and Herman Traff were.
I'd be a little bit surprised if the NHL only invited a limited amount but I suppose that's how the NBA does it. I wouldn't be as surprised if more mid-round guys opted to stay home. Seemingly a lot of them also go to support teammates who are slated to go high. In 2017, I was sitting behind an Owen Sound group on Day 2 (Nick Suzuki plus five other draftees not including Sean Durzi who went undrafted). In 2011, I was surprised to see Mika Zibanejad sitting across the aisle from me during Day 2, but he was supporting Frederik Claesson (5th rounder); Funny moment from when Claesson was drafted, there was a lone voice going nuts from across the arena and it was Gabriel Landeskog.
Location probably is a factor as well. The 2011 Draft in Minnesota was an easy enough drive for those locals. If teams drafted a Minnesota HS kid, they were very sure to mention the name of the high school. There was a comical moment in the 7th round when Devils head scout David Conte announced they were taking "from Benilde-St. Margaret's High School" and then blanked on the name. He hastily covered the mic and asked the table "What's his name?" which ended up being audible to everybody in attendance. Patrick Daly was there to receive the Devils jersey.