Haven't seen anyone mention one big difference yet - the cost to trade a "transaction fee" mutual fund.
At Vanguard, you can get 25 free trades (including tx-fee mutual funds) per year at the Flagship level ($1M+ in VG-branded assets). That's not inconsequential when comparing to FIDO, who I believe still charges $75 (!!!! who on earth still charges $75 per transaction?!) per fund purchase and Schwab, who charges up to $49.95. Fund sales are (I believe) transaction cost free at FIDO and incur an additional $49.95 fee at Schwab.
Those 25 "free" trades on funds that are not NTF can add up to nearly $2K ($1,875) per year.
As others have mentioned up thread, you can also hold a wide variety of popular VG funds like Wellesley, Wellington, Tax Managed Balanced and others far easier and free, (vs paying transaction fees) at VG.
All that said, there are some real trade-offs using VG. The biggest, IMHO, is no 24x7 customer service. They're only reachable M-F, 8-8. That can be a big deal when you have a concern about an account over a weekend and need to wait until Monday at 8 ET to reach them..
VG is also WAY behind FIDO and Schwab on account security. There's currently no secure 2FA - just 2FA via text, which can be easily compromised by SIM hacks. (FIDO, on the other hand, uses Symantec VIP Access that generates a random number every 60 seconds. WAY more secure). Many of us have requested that VG get with the times and implement something like VIP Access and despite repeated requests, VG just doesn't appear to care.
VG does offer a way to restrict logon access to only one computer, but that feature frequently doesn't work. Just happened to me yesterday - tried to log on, and the VG website didn't recognize my PC and wouldn't let me in. So, had to call to get access restored. Fortunately, it was during their (very limited) CS hours. I would have been SOL if it had been a weekend.
It's also taking a lot longer recently to reach a live rep at VG. I had to do a callback (about 10 min wait) yesterday. I seem to get FIDO reps live every time I call them (retail, not 401K) FWIW.
I'd be tempted to consolidate at FIDO or Schwab but the Mutual Fund fees (and ability to have Admiral Wellesley and Wellington among other VG Admiral funds without trading fees) is a biggy to me as I have a number of actively managed funds from companies like PIMCO, Dodge & Cox and others that I don't want to give up..(heresy, I know..), and I don't want to pay nearly $2K / year in MF trading fees at FIDO if I decide to move things around..
ETA - you can also buy the Institutional share class of popular PIMCO funds at VG (like PIMCO Income) with a $25K minimum at VG. Minimums are $1M elsewhere on those Institutional share classes..PIMCO funds usually have very high ERs, and the only class worth even thinking of holding is Institutional for their lower (but still comparatively/ridiculously high) ERs.